JP5982189B2 - Photocatalyst for water splitting - Google Patents
Photocatalyst for water splitting Download PDFInfo
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- JP5982189B2 JP5982189B2 JP2012136156A JP2012136156A JP5982189B2 JP 5982189 B2 JP5982189 B2 JP 5982189B2 JP 2012136156 A JP2012136156 A JP 2012136156A JP 2012136156 A JP2012136156 A JP 2012136156A JP 5982189 B2 JP5982189 B2 JP 5982189B2
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- 239000011941 photocatalyst Substances 0.000 title claims description 100
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 title claims description 93
- 239000012071 phase Substances 0.000 claims description 124
- 239000013078 crystal Substances 0.000 claims description 108
- 239000002131 composite material Substances 0.000 claims description 92
- 239000010936 titanium Substances 0.000 claims description 83
- 238000000034 method Methods 0.000 claims description 32
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 claims description 26
- DSAJWYNOEDNPEQ-UHFFFAOYSA-N barium atom Chemical compound [Ba] DSAJWYNOEDNPEQ-UHFFFAOYSA-N 0.000 claims description 26
- 229910052719 titanium Inorganic materials 0.000 claims description 15
- 239000002243 precursor Substances 0.000 claims description 14
- 238000010304 firing Methods 0.000 claims description 11
- 238000006116 polymerization reaction Methods 0.000 claims description 11
- 229910052788 barium Inorganic materials 0.000 claims description 10
- 239000002994 raw material Substances 0.000 claims description 8
- 238000010532 solid phase synthesis reaction Methods 0.000 claims description 8
- 238000004519 manufacturing process Methods 0.000 claims description 4
- 230000000694 effects Effects 0.000 description 47
- 230000000052 comparative effect Effects 0.000 description 33
- 238000006243 chemical reaction Methods 0.000 description 28
- AYJRCSIUFZENHW-UHFFFAOYSA-L barium carbonate Chemical compound [Ba+2].[O-]C([O-])=O AYJRCSIUFZENHW-UHFFFAOYSA-L 0.000 description 24
- VXUYXOFXAQZZMF-UHFFFAOYSA-N titanium(IV) isopropoxide Chemical compound CC(C)O[Ti](OC(C)C)(OC(C)C)OC(C)C VXUYXOFXAQZZMF-UHFFFAOYSA-N 0.000 description 22
- JRPBQTZRNDNNOP-UHFFFAOYSA-N barium titanate Chemical compound [Ba+2].[Ba+2].[O-][Ti]([O-])([O-])[O-] JRPBQTZRNDNNOP-UHFFFAOYSA-N 0.000 description 20
- 229910002113 barium titanate Inorganic materials 0.000 description 20
- 239000000203 mixture Substances 0.000 description 20
- 239000011651 chromium Substances 0.000 description 17
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 10
- 239000010948 rhodium Substances 0.000 description 10
- LYCAIKOWRPUZTN-UHFFFAOYSA-N Ethylene glycol Chemical compound OCCO LYCAIKOWRPUZTN-UHFFFAOYSA-N 0.000 description 9
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 9
- 239000001257 hydrogen Substances 0.000 description 9
- 229910052739 hydrogen Inorganic materials 0.000 description 9
- 239000001301 oxygen Substances 0.000 description 9
- 229910052760 oxygen Inorganic materials 0.000 description 9
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 description 8
- 239000000126 substance Substances 0.000 description 8
- KRKNYBCHXYNGOX-UHFFFAOYSA-N citric acid Chemical compound OC(=O)CC(O)(C(O)=O)CC(O)=O KRKNYBCHXYNGOX-UHFFFAOYSA-N 0.000 description 7
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- 229910052759 nickel Inorganic materials 0.000 description 5
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 4
- 238000001354 calcination Methods 0.000 description 4
- 229910052741 iridium Inorganic materials 0.000 description 4
- 230000031700 light absorption Effects 0.000 description 4
- 238000011068 loading method Methods 0.000 description 4
- 229910052703 rhodium Inorganic materials 0.000 description 4
- 239000004408 titanium dioxide Substances 0.000 description 4
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 3
- GVHCUJZTWMCYJM-UHFFFAOYSA-N chromium(3+);trinitrate;nonahydrate Chemical compound O.O.O.O.O.O.O.O.O.[Cr+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O GVHCUJZTWMCYJM-UHFFFAOYSA-N 0.000 description 3
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- 238000006722 reduction reaction Methods 0.000 description 3
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 3
- 239000002904 solvent Substances 0.000 description 3
- 238000005979 thermal decomposition reaction Methods 0.000 description 3
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 2
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- 238000010521 absorption reaction Methods 0.000 description 2
- 239000000654 additive Substances 0.000 description 2
- 230000000996 additive effect Effects 0.000 description 2
- 229960004543 anhydrous citric acid Drugs 0.000 description 2
- 229910052786 argon Inorganic materials 0.000 description 2
- IWOUKMZUPDVPGQ-UHFFFAOYSA-N barium nitrate Chemical compound [Ba+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O IWOUKMZUPDVPGQ-UHFFFAOYSA-N 0.000 description 2
- 239000012159 carrier gas Substances 0.000 description 2
- 229910052802 copper Inorganic materials 0.000 description 2
- 238000002156 mixing Methods 0.000 description 2
- 239000004570 mortar (masonry) Substances 0.000 description 2
- AOPCKOPZYFFEDA-UHFFFAOYSA-N nickel(2+);dinitrate;hexahydrate Chemical compound O.O.O.O.O.O.[Ni+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O AOPCKOPZYFFEDA-UHFFFAOYSA-N 0.000 description 2
- 238000007254 oxidation reaction Methods 0.000 description 2
- 229910052763 palladium Inorganic materials 0.000 description 2
- 230000001699 photocatalysis Effects 0.000 description 2
- 229910052697 platinum Inorganic materials 0.000 description 2
- 230000006798 recombination Effects 0.000 description 2
- 229910052707 ruthenium Inorganic materials 0.000 description 2
- 238000003980 solgel method Methods 0.000 description 2
- 239000000243 solution Substances 0.000 description 2
- 238000001228 spectrum Methods 0.000 description 2
- 229910052715 tantalum Inorganic materials 0.000 description 2
- QDZRBIRIPNZRSG-UHFFFAOYSA-N titanium nitrate Chemical compound [O-][N+](=O)O[Ti](O[N+]([O-])=O)(O[N+]([O-])=O)O[N+]([O-])=O QDZRBIRIPNZRSG-UHFFFAOYSA-N 0.000 description 2
- TYLYVJBCMQFRCB-UHFFFAOYSA-K trichlororhodium;trihydrate Chemical compound O.O.O.[Cl-].[Cl-].[Cl-].[Rh+3] TYLYVJBCMQFRCB-UHFFFAOYSA-K 0.000 description 2
- WQNHWIYLCRZRLR-UHFFFAOYSA-N 2-(3-hydroxy-2,5-dioxooxolan-3-yl)acetic acid Chemical compound OC(=O)CC1(O)CC(=O)OC1=O WQNHWIYLCRZRLR-UHFFFAOYSA-N 0.000 description 1
- 229910002012 Aerosil® Inorganic materials 0.000 description 1
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 description 1
- KRKNYBCHXYNGOX-UHFFFAOYSA-K Citrate Chemical compound [O-]C(=O)CC(O)(CC([O-])=O)C([O-])=O KRKNYBCHXYNGOX-UHFFFAOYSA-K 0.000 description 1
- 229910020599 Co 3 O 4 Inorganic materials 0.000 description 1
- MYMOFIZGZYHOMD-UHFFFAOYSA-N Dioxygen Chemical compound O=O MYMOFIZGZYHOMD-UHFFFAOYSA-N 0.000 description 1
- 229910003297 Ni(NO3)3·6H2O Inorganic materials 0.000 description 1
- 229910003266 NiCo Inorganic materials 0.000 description 1
- 229910010413 TiO 2 Inorganic materials 0.000 description 1
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 1
- 229910021529 ammonia Inorganic materials 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 229910052787 antimony Inorganic materials 0.000 description 1
- RQPZNWPYLFFXCP-UHFFFAOYSA-L barium dihydroxide Chemical compound [OH-].[OH-].[Ba+2] RQPZNWPYLFFXCP-UHFFFAOYSA-L 0.000 description 1
- 229910001863 barium hydroxide Inorganic materials 0.000 description 1
- AYJRCSIUFZENHW-DEQYMQKBSA-L barium(2+);oxomethanediolate Chemical compound [Ba+2].[O-][14C]([O-])=O AYJRCSIUFZENHW-DEQYMQKBSA-L 0.000 description 1
- BJXXCWDIBHXWOH-UHFFFAOYSA-N barium(2+);oxygen(2-);tantalum(5+) Chemical compound [O-2].[O-2].[O-2].[O-2].[O-2].[O-2].[O-2].[O-2].[O-2].[O-2].[O-2].[O-2].[O-2].[O-2].[O-2].[Ba+2].[Ba+2].[Ba+2].[Ba+2].[Ba+2].[Ta+5].[Ta+5].[Ta+5].[Ta+5] BJXXCWDIBHXWOH-UHFFFAOYSA-N 0.000 description 1
- 244000309464 bull Species 0.000 description 1
- 229910052793 cadmium Inorganic materials 0.000 description 1
- 238000011088 calibration curve Methods 0.000 description 1
- 230000003197 catalytic effect Effects 0.000 description 1
- 239000000919 ceramic Substances 0.000 description 1
- 239000003153 chemical reaction reagent Substances 0.000 description 1
- 229960004106 citric acid Drugs 0.000 description 1
- 238000000975 co-precipitation Methods 0.000 description 1
- IVMYJDGYRUAWML-UHFFFAOYSA-N cobalt(II) oxide Inorganic materials [Co]=O IVMYJDGYRUAWML-UHFFFAOYSA-N 0.000 description 1
- 239000000498 cooling water Substances 0.000 description 1
- 239000011258 core-shell material Substances 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000007865 diluting Methods 0.000 description 1
- 229910001882 dioxygen Inorganic materials 0.000 description 1
- 238000000921 elemental analysis Methods 0.000 description 1
- 230000005496 eutectics Effects 0.000 description 1
- 230000001747 exhibiting effect Effects 0.000 description 1
- 239000000446 fuel Substances 0.000 description 1
- 229910052733 gallium Inorganic materials 0.000 description 1
- 238000004868 gas analysis Methods 0.000 description 1
- 239000011521 glass Substances 0.000 description 1
- 229910052737 gold Inorganic materials 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 238000001027 hydrothermal synthesis Methods 0.000 description 1
- 229910052738 indium Inorganic materials 0.000 description 1
- 229910000765 intermetallic Inorganic materials 0.000 description 1
- 229910052745 lead Inorganic materials 0.000 description 1
- 229910052749 magnesium Inorganic materials 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
- 239000002923 metal particle Substances 0.000 description 1
- 239000002808 molecular sieve Substances 0.000 description 1
- 229910052758 niobium Inorganic materials 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 238000005504 petroleum refining Methods 0.000 description 1
- 238000010587 phase diagram Methods 0.000 description 1
- 239000000843 powder Substances 0.000 description 1
- 238000000634 powder X-ray diffraction Methods 0.000 description 1
- 238000010298 pulverizing process Methods 0.000 description 1
- 239000010453 quartz Substances 0.000 description 1
- 230000005855 radiation Effects 0.000 description 1
- 238000010405 reoxidation reaction Methods 0.000 description 1
- QAMPSLDLJHRGPM-UHFFFAOYSA-N rhodium;trihydrate Chemical compound O.O.O.[Rh] QAMPSLDLJHRGPM-UHFFFAOYSA-N 0.000 description 1
- 238000005070 sampling Methods 0.000 description 1
- 229910052709 silver Inorganic materials 0.000 description 1
- URGAHOPLAPQHLN-UHFFFAOYSA-N sodium aluminosilicate Chemical compound [Na+].[Al+3].[O-][Si]([O-])=O.[O-][Si]([O-])=O URGAHOPLAPQHLN-UHFFFAOYSA-N 0.000 description 1
- 239000006104 solid solution Substances 0.000 description 1
- 239000000758 substrate Substances 0.000 description 1
- 239000000725 suspension Substances 0.000 description 1
- 238000001308 synthesis method Methods 0.000 description 1
- GUVRBAGPIYLISA-UHFFFAOYSA-N tantalum atom Chemical compound [Ta] GUVRBAGPIYLISA-UHFFFAOYSA-N 0.000 description 1
- 229910052721 tungsten Inorganic materials 0.000 description 1
- 238000010792 warming Methods 0.000 description 1
- 229910052725 zinc Inorganic materials 0.000 description 1
Classifications
-
- 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
Landscapes
- Oxygen, Ozone, And Oxides In General (AREA)
- Catalysts (AREA)
Description
本発明は、太陽光を利用した水分解反応を行うことにより水素および／または酸素を製造可能な光水分解反応に特に好適に用いられる光触媒に関する。 The present invention relates to a photocatalyst that is particularly preferably used for a photohydrolysis reaction that can produce hydrogen and / or oxygen by performing a water splitting reaction using sunlight.
太陽エネルギーなどの再生可能エネルギーを利用した高性能な光エネルギー変換システムを実用化することは、地球温暖化の抑制、および枯渇しつつある化石資源依存からの脱却を目指す観点から、近年になって急激にその重要性が増している。中でも、太陽エネルギーを用いて水を分解し水素を製造する技術は、現行の石油精製、アンモニア、メタノールの原料供給技術としてのみならず、燃料電池をベースとした来たる水素エネルギー社会において、必須とされる技術である。 In recent years, the practical application of high-performance light energy conversion systems that use renewable energy such as solar energy has been aimed at controlling global warming and moving away from the depletion of fossil resources. Its importance is increasing rapidly. Above all, the technology that decomposes water using solar energy to produce hydrogen is indispensable not only in the current petroleum refining, ammonia and methanol raw material supply technology, but also in the future hydrogen energy society based on fuel cells. Technology.
例えば、光触媒を用いることで、太陽エネルギーを利用して水を分解し、効率的に水素を製造することができる（非特許文献１等）。この場合に用いられる光触媒の一つにチタン酸バリウム系光触媒がある。チタン酸バリウム系光触媒は紫外光に応答して水分解活性を示すことが知られており、特にＢａＴｉ４Ｏ９が有望とされている（非特許文献２等）。 For example, by using a photocatalyst, water can be decomposed using solar energy and hydrogen can be efficiently produced (Non-patent Document 1, etc.). One of the photocatalysts used in this case is a barium titanate photocatalyst. Barium titanate-based photocatalysts are known to exhibit water-splitting activity in response to ultraviolet light, and BaTi 4 O 9 is particularly promising (Non-Patent Document 2, etc.).
しかしながら、チタン酸バリウム系の光触媒にあっては、水分解活性が必ずしも十分ではなかった。 However, the water decomposition activity is not always sufficient for the barium titanate photocatalyst.
一方、タンタル酸バリウム等のその他光触媒についても研究されてはいるが（非特許文献３等）、やはり活性は十分でなく、また、材料として高価なタンタルを使用しなければならないという欠点があった。 On the other hand, although other photocatalysts such as barium tantalate have been studied (Non-patent Document 3, etc.), the activity is still insufficient, and there is a disadvantage that expensive tantalum must be used as a material. .
そこで本発明は、バリウム、チタンという資源が豊富で比較的安価な材料から製造可能であり、水分解活性が向上された水分解用光触媒を提供することを課題とする。 Therefore, an object of the present invention is to provide a photocatalyst for water splitting that can be manufactured from a relatively inexpensive material rich in resources such as barium and titanium and has improved water splitting activity.
本発明者らは、上記の課題を解決すべく鋭意検討した結果、以下の知見を得た。
（１）チタン酸バリウム系光触媒において、組成比（Ｔｉ／Ｂａ）を、光触媒活性を示すものとして従来からよく知られていた結晶相の量論比ではなく、量論比からずれた範囲となるようにし、複数種の結晶相を生成させることで、光触媒の水分解活性が向上する。
（２）複数の結晶相において、主相がＢａＴｉ４Ｏ９結晶相であり、これ以外にＢａＴｉ２Ｏ５結晶相を含む混合相とすることで、光触媒の水分解活性が向上する。
（３）或いは、複数の結晶相において、主相がＢａＴｉ４Ｏ９結晶相であり、これ以外にＢａＴｉ２Ｏ５結晶相およびＢａ４Ｔｉ１３Ｏ３０結晶相を含む混合相とすることで、光触媒の水分解活性が向上する。
（４）或いは、複数の結晶相において、主相がＢａ４Ｔｉ１３Ｏ３０結晶相であり、これ以外にＢａＴｉ４Ｏ９結晶相およびＢａＴｉ２Ｏ５結晶相を含む混合相とすることで、光触媒の水分解活性が向上する。
（５）バリウム原子に対するチタン原子のモル比（Ｔｉ／Ｂａ）が３＜Ｔｉ／Ｂａ＜４の場合に、特に光触媒の水分解活性が向上する。
As a result of intensive studies to solve the above problems, the present inventors have obtained the following knowledge.
(1) In a barium titanate photocatalyst, the composition ratio (Ti / Ba) is not a stoichiometric ratio of a crystal phase that has been well known so far as exhibiting photocatalytic activity, but a range deviated from the stoichiometric ratio Thus, the water splitting activity of the photocatalyst is improved by generating a plurality of types of crystal phases.
(2) In a plurality of crystal phases, the main phase is a BaTi 4 O 9 crystal phase, and a mixed phase containing a BaTi 2 O 5 crystal phase in addition to this improves the water splitting activity of the photocatalyst.
(3) Alternatively, in a plurality of crystal phases, the main phase is a BaTi 4 O 9 crystal phase, and in addition to this, a mixed phase including a BaTi 2 O 5 crystal phase and a Ba 4 Ti 13 O 30 crystal phase, The water splitting activity of the photocatalyst is improved.
(4) Alternatively, in a plurality of crystal phases, the main phase is a Ba 4 Ti 13 O 30 crystal phase, and in addition to this, a mixed phase containing a BaTi 4 O 9 crystal phase and a BaTi 2 O 5 crystal phase is obtained. The water splitting activity of the photocatalyst is improved.
(5) When the molar ratio of titanium atom to barium atom (Ti / Ba) is 3 <Ti / Ba <4, the water splitting activity of the photocatalyst is particularly improved.
本発明は上記の知見に基づいてなされたものである。すなわち、
本発明の第１の態様は、チタンおよびバリウムを含む複合酸化物と助触媒とを含有する水分解用光触媒であって、複合酸化物は、ＢａＴｉ４Ｏ９結晶相とＢａＴｉ２Ｏ５結晶相とを含み、ＢａＴｉ４Ｏ９結晶相とＢａＴｉ２Ｏ５結晶相との合計を１００モル％とした場合において、ＢａＴｉ４Ｏ９結晶相の含有比が６０モル％以上であり、かつ、バリウム原子に対するチタン原子のモル比（Ｔｉ／Ｂａ）が３＜Ｔｉ／Ｂａ＜４である、水分解用光触媒である。
The present invention has been made based on the above findings. That is,
A first aspect of the present invention is a water splitting photocatalyst containing a composite oxide containing titanium and barium and a cocatalyst, wherein the composite oxide comprises a BaTi 4 O 9 crystal phase and a BaTi 2 O 5 crystal phase. In the case where the total of the BaTi 4 O 9 crystal phase and the BaTi 2 O 5 crystal phase is 100 mol%, the content ratio of the BaTi 4 O 9 crystal phase is 60 mol% or more, and a barium atom It is a photocatalyst for water splitting, wherein the molar ratio of titanium atom to Ti (Ba / Ba) is 3 <Ti / Ba <4.
本発明の第２の態様は、チタンおよびバリウムを含む複合酸化物と助触媒とを含有する水分解用光触媒であって、複合酸化物は、ＢａＴｉ４Ｏ９結晶相とＢａＴｉ２Ｏ５結晶相とＢａ４Ｔｉ１３Ｏ３０結晶相とを含み、ＢａＴｉ４Ｏ９結晶相とＢａＴｉ２Ｏ５結晶相とＢａ４Ｔｉ１３Ｏ３０結晶相との合計を１００モル％とした場合において、ＢａＴｉ４Ｏ９結晶相またはＢａ４Ｔｉ１３Ｏ３０結晶相の含有比が６０モル％以上であり、かつ、バリウム原子に対するチタン原子のモル比（Ｔｉ／Ｂａ）が３＜Ｔｉ／Ｂａ＜４である、水分解用光触媒である。 The second aspect of the present invention is a water splitting photocatalyst containing a composite oxide containing titanium and barium and a cocatalyst, wherein the composite oxide comprises a BaTi 4 O 9 crystal phase and a BaTi 2 O 5 crystal phase. And the Ba 4 Ti 13 O 30 crystal phase, and the total of the BaTi 4 O 9 crystal phase, the BaTi 2 O 5 crystal phase and the Ba 4 Ti 13 O 30 crystal phase is 100 mol%, the BaTi 4 O 9 The crystal phase or the content ratio of the Ba 4 Ti 13 O 30 crystal phase is 60 mol% or more, and the molar ratio of titanium atoms to barium atoms (Ti / Ba) is 3 <Ti / Ba <4 It is a photocatalyst for decomposition.
本発明の第１の態様および第２の態様のいずれにおいても、ＢａＴｉ２Ｏ５結晶相の含有比が１０モル％以上であることが好ましい。 In both the first aspect and the second aspect of the present invention, the content ratio of the BaTi 2 O 5 crystal phase is preferably 10 mol% or more.
本発明の第１の態様および第２の態様のいずれにおいても、助触媒が、Ｎｉ酸化物、およびＲｈ−Ｃｒ複合酸化物より選ばれる１種以上であることが好ましい。 In any of the first and second aspects of the present invention, the promoter is preferably at least one selected from Ni oxide and Rh—Cr composite oxide.
本発明の第１の態様および第２の態様のいずれにおいても、複合酸化物が、チタン原子を含む原料とバリウム原子を含む原料とを、バリウム原子に対するチタン原子のモル比（Ｔｉ／Ｂａ）が３＜Ｔｉ／Ｂａ＜４となるように混合し、前駆体とした後、焼成して得たものであることが特に好ましい。 In any of the first aspect and the second aspect of the present invention, the composite oxide comprises a raw material containing a titanium atom and a raw material containing a barium atom, wherein the molar ratio of titanium atoms to barium atoms (Ti / Ba) is It is particularly preferable that it is obtained by firing after mixing so that 3 <Ti / Ba <4 to form a precursor.
本発明の第１の態様および第２の態様のいずれにおいても、複合酸化物が、固相法または錯体重合法によって得られたものであることが好ましい。 In any of the first aspect and the second aspect of the present invention, the composite oxide is preferably obtained by a solid phase method or a complex polymerization method.
上記の本発明においては、例えば、Ｘ線回折装置等を用いて結晶構造解析することにより、得られるピーク比に基づいて、複数の結晶相に対する一の結晶相の含有比（モル比）を特定することができる。
また、例えば、蛍光Ｘ線分析装置等を用いて元素分析することにより、複合酸化物におけるバリウム原子に対するチタン原子のモル比（Ｔｉ／Ｂａ）を特定することができる。
In the present invention, for example, by analyzing the crystal structure using an X-ray diffractometer or the like, the content ratio (molar ratio) of one crystal phase to a plurality of crystal phases is specified based on the obtained peak ratio. can do.
Further, for example, by performing elemental analysis using a fluorescent X-ray analyzer or the like, the molar ratio (Ti / Ba) of titanium atoms to barium atoms in the composite oxide can be specified.
本発明においては、チタン酸バリウムの組成比（Ｔｉ／Ｂａ）を良く知られた結晶相の量論比ではなく、量論比から意図的にずらした３＜Ｔｉ／Ｂａ＜４の範囲として、所定の結晶相が主相であり、かつ、その他の所定の結晶相をも含む混合相からなる複合酸化物とすることで、チタン酸バリウム系光触媒の水分解活性を従来よりも向上させている。すなわち、本発明によれば、バリウム、チタンという資源が豊富で比較的安価な材料から製造可能であり、水分解活性が向上された水分解用光触媒を提供することができる。 In the present invention, the composition ratio of barium titanate (Ti / Ba) is not a well-known stoichiometric ratio, but a range of 3 <Ti / Ba <4 intentionally shifted from the stoichiometric ratio, The water decomposition activity of the barium titanate-based photocatalyst is improved as compared with the prior art by using a composite oxide composed of a mixed phase including a predetermined crystal phase as a main phase and also including other predetermined crystal phases. . That is, according to the present invention, it is possible to provide a photocatalyst for water splitting which can be manufactured from a relatively inexpensive material rich in resources such as barium and titanium and has improved water splitting activity.
本発明の水分解用光触媒は、チタンおよびバリウムを含む複合酸化物と助触媒とを含有する水分解用光触媒であり、複合酸化物におけるチタン酸バリウムの組成比（Ｔｉ／Ｂａ）を良く知られた結晶相の量論比ではなく、量論比から意図的にずらした３＜Ｔｉ／Ｂａ＜４の範囲として、所定の結晶相が主相であり、かつ、その他の所定の結晶相をも含む混合相とされた複合酸化物としたことに特徴を有する。 The photocatalyst for water splitting of the present invention is a photocatalyst for water splitting containing a composite oxide containing titanium and barium and a cocatalyst, and the composition ratio (Ti / Ba) of barium titanate in the composite oxide is well known. In the range of 3 <Ti / Ba <4 that is intentionally shifted from the stoichiometric ratio, not the stoichiometric ratio of the crystal phase, the predetermined crystal phase is the main phase and other predetermined crystal phases are also included. It is characterized in that it is a composite oxide containing mixed phases.
１．複合酸化物
本発明の第１実施形態においては、当該複合酸化物は、ＢａＴｉ４Ｏ９結晶相とＢａＴｉ２Ｏ５結晶相とを含み、ＢａＴｉ４Ｏ９結晶相とＢａＴｉ２Ｏ５結晶相との合計を１００モル％とした場合において、ＢａＴｉ４Ｏ９結晶相の含有比が６０モル％以上であり、かつ、バリウム原子に対するチタン原子のモル比（Ｔｉ／Ｂａ）が３＜Ｔｉ／Ｂａ＜４であることに特徴を有する。
1. Composite Oxide In the first embodiment of the present invention, the composite oxide includes a BaTi 4 O 9 crystal phase and a BaTi 2 O 5 crystal phase, and a BaTi 4 O 9 crystal phase and a BaTi 2 O 5 crystal phase. In the case where the total amount is 100 mol%, the content ratio of the BaTi 4 O 9 crystal phase is 60 mol% or more, and the molar ratio of titanium atoms to barium atoms (Ti / Ba) is 3 <Ti / Ba < It is characterized by being 4.
本発明の第２実施形態においては、当該複合酸化物は、ＢａＴｉ４Ｏ９結晶相とＢａＴｉ２Ｏ５結晶相とＢａ４Ｔｉ１３Ｏ３０結晶相とを含み、ＢａＴｉ４Ｏ９結晶相とＢａＴｉ２Ｏ５結晶相とＢａ４Ｔｉ１３Ｏ３０結晶相の合計を１００モル％とした場合において、ＢａＴｉ４Ｏ９結晶相またはＢａ４Ｔｉ１３Ｏ３０結晶相の含有比が６０モル％以上であり、かつ、バリウム原子に対するチタン原子のモル比（Ｔｉ／Ｂａ）が３＜Ｔｉ／Ｂａ＜４であることに特徴を有する。 In the second embodiment of the present invention, the composite oxide includes a BaTi 4 O 9 crystal phase, a BaTi 2 O 5 crystal phase, a Ba 4 Ti 13 O 30 crystal phase, and a BaTi 4 O 9 crystal phase and a BaTi. When the total of the 2 O 5 crystal phase and the Ba 4 Ti 13 O 30 crystal phase is 100 mol%, the content ratio of the BaTi 4 O 9 crystal phase or the Ba 4 Ti 13 O 30 crystal phase is 60 mol% or more. And the molar ratio of titanium atom to barium atom (Ti / Ba) is 3 <Ti / Ba <4.
上記第１実施形態および第２実施形態のいずれの形態に係る複合酸化物においても、ＢａＴｉ２Ｏ５結晶相の含有比が１０モル％以上であることが好ましい。ＢａＴｉ２Ｏ５結晶相の含有比の上限については、４０モル％以下、好ましくは３５モル％以下、より好ましくは３０モル％以下である。ＢａＴｉ２Ｏ５結晶相の含有比を当該範囲内とすることで、光触媒の水分解活性を一層向上させることができる。 In the composite oxide according to any of the first embodiment and the second embodiment, the content ratio of the BaTi 2 O 5 crystal phase is preferably 10 mol% or more. The upper limit of the content ratio of BaTi 2 O 5 crystalline phase, 40 mol% or less, preferably 35 mol% or less, more preferably 30 mol% or less. By making the content ratio of the BaTi 2 O 5 crystal phase within the range, the water splitting activity of the photocatalyst can be further improved.
上記の複合酸化物は、例えば、チタン原子を含む原料とバリウム原子を含む原料とを、バリウム原子に対するチタン原子のモル比（Ｔｉ／Ｂａ）が３＜Ｔｉ／Ｂａ＜４となるように混合し、前駆体とした後、焼成することによって容易に得ることができる。焼成条件等については、例えば、Ｊ．Ｊ.Ｒｉｔｔｅｒ ｅｔ ａｌ．，Ｊｏｕｒｎａｌ ｏｆｔｈｅ Ａｍｅｒｉｃａｎ Ｃｅｒａｍｉｃ Ｓｏｃｉｅｔｙ， ｖｏｌ６９，Ｎｏ．２，１５５−１６２（１９８６）に記載されたようなＢａとＴｉの２元相図等を参照しつつ決定することが好ましい。例えば、本発明者らの知見によれば、下記表１に示すように、錯体重合法において上記モル比を３〜３．５程度とし、かつ焼成温度を低温（例えば、８５０℃以下）とすることで、第１実施形態に係る複合酸化物を容易に得ることができる。一方、同じく錯体重合法において上記モル比を３．５〜４程度とし、焼成温度を低温（例えば、８５０℃以下）とすることで、第２実施形態に係る複合酸化物を容易に得ることができる。さらに、固相法において、上記モル比を３．５〜４程度とし、かつ焼成温度を高温（例えば、８５０℃以上）とすることで、第２実施形態に係る複合酸化物を容易に得ることができる。詳しくは後述する。 In the composite oxide, for example, a raw material containing titanium atoms and a raw material containing barium atoms are mixed so that the molar ratio of titanium atoms to barium atoms (Ti / Ba) is 3 <Ti / Ba <4. The precursor can be easily obtained by firing. Regarding the firing conditions and the like, see, for example, J. Ritter et al. , Journal of the American Ceramic Society, vol. 2,155-162 (1986), and preferably determined with reference to a binary phase diagram of Ba and Ti. For example, according to the knowledge of the present inventors, as shown in Table 1 below, in the complex polymerization method, the molar ratio is about 3 to 3.5, and the firing temperature is low (for example, 850 ° C. or lower). Thus, the composite oxide according to the first embodiment can be easily obtained. On the other hand, in the complex polymerization method, the complex ratio according to the second embodiment can be easily obtained by setting the molar ratio to about 3.5 to 4 and setting the firing temperature to a low temperature (for example, 850 ° C. or lower). it can. Furthermore, in the solid phase method, the composite oxide according to the second embodiment can be easily obtained by setting the molar ratio to about 3.5 to 4 and setting the firing temperature to a high temperature (for example, 850 ° C. or higher). Can do. Details will be described later.
チタン原子を含む原料としては二酸化チタンや硝酸チタン、チタンテトライソプロポキシド等、またバリウム原子を含む原料としては炭酸バリウムや硝酸バリウム、水酸化バリウム等、固相法やゾル・ゲル法（例えば錯体重合法）等の複合酸化物を生成させ得る公知の方法（例えば、Ｉｎｏｕｅ，Ｙ．ｅｔ ａｌ．Ｊ．Ｃｈｅｍ．Ｓｏｃ．，Ｆａｒａｄａｙ ｔｒａｎｓ．１９９４，９０（５），７９７−８０２やＫａｋｉｈａｎａ，Ｍ．ｅｔ ａｌ．Ｂｕｌｌ．Ｃｈｅｍ．Ｓｏｃ．Ｊｐｎ．１９９９，７２７（７），１４２７−１４４３に記載の方法を適用することができる。）に適した原料であれば、特に限定されるものではない。 Materials containing titanium atoms include titanium dioxide, titanium nitrate, titanium tetraisopropoxide, and materials containing barium atoms such as barium carbonate, barium nitrate, barium hydroxide, etc. Known methods (for example, Inoue, Y. et al. J. Chem. Soc., Faraday trans. 1994, 90 (5), 797-802, Kakihana, M. et al.). et al. Bull. Chem. Soc. Jpn. 1999, 727 (7), 1427-1443.) The raw material is not particularly limited.
固相法の場合は、例えば、二酸化チタンと炭酸バリウムとを上記モル比となるように混合し前駆体を得て、当該前駆体を空気雰囲気下等の酸素存在下、９００℃以上１１００℃以下、好ましくは９００℃以上１０００℃以下で、５時間以上、好ましくは１０時間以上、より好ましくは２０時間以上焼成することにより、本発明に係る所望の複合酸化物を得ることができる。 In the case of the solid phase method, for example, titanium dioxide and barium carbonate are mixed so as to have the above molar ratio to obtain a precursor, and the precursor is 900 ° C. or higher and 1100 ° C. or lower in the presence of oxygen such as in an air atmosphere. The desired composite oxide according to the present invention can be obtained by firing at 900 ° C. or higher and 1000 ° C. or lower for 5 hours or longer, preferably 10 hours or longer, more preferably 20 hours or longer.
錯体重合法の場合は、例えば、エチレングリコールに、チタンテトライソプロポキシド等のチタン源や、炭酸バリウム等のバリウム源を添加して溶解させ、ここにクエン酸を添加して金属クエン酸錯体を得る。その後温度を重合温度まで上昇させてエステル結合により重合させることでゲルを得て、当該ゲルを熱分解温度（例えば３００℃〜４００℃）にて加熱することで熱分解させて前駆体を得る。当該前駆体を空気雰囲気下等の酸素存在下、７００℃以上９００℃以下、好ましくは７５０℃以上８５０℃以下で、５時間以上、好ましくは１０時間以上焼成することにより、本発明に係る所望の複合酸化物を得ることができる。 In the case of the complex polymerization method, for example, a titanium source such as titanium tetraisopropoxide or a barium source such as barium carbonate is added to ethylene glycol and dissolved, and citric acid is added thereto to form a metal citrate complex. obtain. Thereafter, the temperature is raised to the polymerization temperature and polymerized by an ester bond to obtain a gel, and the gel is thermally decomposed by heating at a thermal decomposition temperature (for example, 300 ° C. to 400 ° C.) to obtain a precursor. The precursor is calcined in the presence of oxygen such as in an air atmosphere at 700 ° C. or higher and 900 ° C. or lower, preferably 750 ° C. or higher and 850 ° C. or lower for 5 hours or longer, preferably 10 hours or longer. A composite oxide can be obtained.
操作が簡便である観点からは、固相法によって本発明に係る複合酸化物を得ることが好ましい。一方で、低温の焼成で容易に所望の複合酸化物を得ることができる観点からは、錯体重合法等のゾル・ゲル法によって本発明に係る複合酸化物を得ることが好ましい。ただし、本発明に係る複合酸化物を得る方法としては、固相法やゾル・ゲル法に限定されるものではない。共沈法や水熱合成法等、各種の酸化物合成方法によって複合酸化物を得ることができる。 From the viewpoint of easy operation, it is preferable to obtain the composite oxide according to the present invention by a solid phase method. On the other hand, from the viewpoint of easily obtaining a desired composite oxide by low-temperature firing, it is preferable to obtain the composite oxide according to the present invention by a sol-gel method such as a complex polymerization method. However, the method for obtaining the composite oxide according to the present invention is not limited to the solid phase method or the sol-gel method. Complex oxides can be obtained by various oxide synthesis methods such as coprecipitation and hydrothermal synthesis.
２．助触媒
上記複合酸化物には、還元反応（水素生成反応）用助触媒或いは酸化反応（酸素生成反応）用助触媒といった助触媒が担持される。
還元反応用助触媒としては、好ましくは、Ｐｔ、Ｐｄ、Ｒｈ、Ｒｕ、Ｎｉ、Ａｕ、Ｆｅ、Ｒｕ−Ｉｒ、Ｎｉ酸化物、ＲｕＯ２、ＩｒＯ２、Ｒｈ２Ｏ３、ＮｉＳ、ＭｏＳ２、ＮｉＭｏＳ、Ｃｒ−Ｒｈ複合酸化物、コアシェル型Ｒｈ／Ｃｒ２Ｏ３、Ｐｔ／Ｃｒ２Ｏ３等を挙げることができる。このうち、Ｎｉ酸化物またはＲｈ−Ｃｒ複合酸化物が特に好ましい。
酸化反応用助触媒としては、好ましくは、Ｍｇ、Ｔｉ、Ｍｎ、Ｆｅ、Ｃｏ、Ｎｉ、Ｃｕ、Ｇａ、Ｒｕ、Ｒｈ、Ｐｄ、Ａｇ、Ｃｄ、Ｉｎ、Ｃｅ、Ｔａ、Ｗ、Ｉｒ、ＰｔまたはＰｂの金属、該金属の金属間化合物、固溶体、共晶体、もしくは該金属の多元金属粒子、該金属の酸化物または複合酸化物であり、より好ましくは、Ｍｎ、Ｃｏ、Ｎｉ、Ｒｕ、Ｒｈ、Ｉｒの金属、これらの酸化物または複合酸化物であり、さらに好ましくは、ＭｎＯ、ＭｎＯ２、Ｍｎ２Ｏ３、Ｍｎ３Ｏ４、ＣｏＯ、Ｃｏ３Ｏ４、ＮｉＣｏ２Ｏ４、ＲｕＯ２、Ｒｈ２Ｏ３、ＩｒＯ２である。この中でも、Ｉｒ酸化物、Ｃｏ酸化物、Ｍｎ酸化物からなる群より選ばれる１種以上が特に好ましい。
2. Co-catalyst A co-catalyst such as a co-catalyst for reduction reaction (hydrogen generation reaction) or a co-catalyst for oxidation reaction (oxygen generation reaction) is supported on the composite oxide.
As the cocatalyst for the reduction reaction, Pt, Pd, Rh, Ru, Ni, Au, Fe, Ru—Ir, Ni oxide, RuO 2 , IrO 2 , Rh 2 O 3 , NiS, MoS 2 , NiMoS are preferable. , Cr—Rh composite oxide, core-shell type Rh / Cr 2 O 3 , Pt / Cr 2 O 3 and the like. Among these, Ni oxide or Rh—Cr composite oxide is particularly preferable.
The oxidation reaction promoter is preferably Mg, Ti, Mn, Fe, Co, Ni, Cu, Ga, Ru, Rh, Pd, Ag, Cd, In, Ce, Ta, W, Ir, Pt or Pb. Metal, intermetallic compound of the metal, solid solution, eutectic, or multicomponent metal particles of the metal, oxide or composite oxide of the metal, and more preferably Mn, Co, Ni, Ru, Rh, Ir metal, an oxide thereof or composite oxides, more preferably, MnO, MnO 2, Mn 2 O 3, Mn 3 O 4, CoO, Co 3 O 4, NiCo 2 O 4, RuO 2, Rh 2 O 3 and IrO 2 . Among these, at least one selected from the group consisting of Ir oxide, Co oxide, and Mn oxide is particularly preferable.
助触媒の量は少なすぎても効果がなく、多すぎると助触媒自身が光を吸収・散乱するなどして光触媒の光吸収を妨げたり、再結合中心として働いたりしてかえって触媒活性が低下してしまう。このような観点から、光触媒への助触媒の担持量は、光触媒を基準（１００質量％）として、好ましくは０．０１質量％以上２０質量％以下、より好ましくは０．０１質量％以上１５質量％以下、特に好ましくは０．０１質量％以上１０質量％以下である。 If the amount of the cocatalyst is too small, there is no effect. If the amount is too large, the cocatalyst itself absorbs and scatters light, thereby preventing the photocatalyst from absorbing light or acting as a recombination center. Resulting in. From such a viewpoint, the amount of the cocatalyst supported on the photocatalyst is preferably 0.01% by mass or more and 20% by mass or less, more preferably 0.01% by mass or more and 15% by mass, based on the photocatalyst (100% by mass). % Or less, particularly preferably 0.01% by mass or more and 10% by mass or less.
複合酸化物への助触媒の担持方法については特に限定されるものではなく、公知の手法をいずれも適用することができる。 The method for supporting the cocatalyst on the composite oxide is not particularly limited, and any known method can be applied.
３．添加物（ドーパント）
本発明に係る水分解用光触媒は、可視光領域の吸収を高めるため、添加物として結晶内部もしくは表面にＮａ、Ｃｒ、Ｍｎ、Ｆｅ、Ｎｉ、Ｃｕ、Ｚｎ、Ｇａ、Ｎｂ、Ｒｈ、Ｓｂ、Ｔａのいずれか１元素以上をドーパントとして含むことができる。ドーパントは少なすぎても効果がなく、多すぎると再結合中心として働いてしまい触媒活性が低下する。したがって母体であるチタン酸バリウム混合相に対して０．０１質量％以上５質量％以下程度が好ましい。
3. Additive (dopant)
The photocatalyst for water splitting according to the present invention enhances absorption in the visible light region, and as an additive, Na, Cr, Mn, Fe, Ni, Cu, Zn, Ga, Nb, Rh, Sb, Ta, inside the crystal or on the surface Any one or more of these can be included as a dopant. If the amount of dopant is too small, there is no effect. If the amount is too large, it acts as a recombination center and the catalytic activity decreases. Therefore, about 0.01 mass% or more and 5 mass% or less are preferable with respect to the base barium titanate mixed phase.
以上のように、本発明に係る水分解用光触媒は、複合酸化物におけるチタン酸バリウムの組成比（Ｔｉ／Ｂａ）を良く知られた結晶相の量論比ではなく、量論比から意図的にずらした３＜Ｔｉ／Ｂａ＜４の範囲として、所定の結晶相が主相であり、かつ、その他の所定の結晶相をも含む混合相とされた複合酸化物としたことにより、従来のチタン酸バリウム系光触媒と比べて、水分解活性を向上させることができる。 As described above, the photocatalyst for water splitting according to the present invention intentionally uses the stoichiometric ratio, not the stoichiometric ratio of the crystal phase, rather than the well-known stoichiometric ratio of the barium titanate in the composite oxide (Ti / Ba). In the range of 3 <Ti / Ba <4 shifted to the above, a composite oxide in which a predetermined crystal phase is a main phase and a mixed phase including other predetermined crystal phases is used. Compared with a barium titanate photocatalyst, the water splitting activity can be improved.
本発明に係る水分解用光触媒を実際に水の分解に使用する場合において、光触媒の形態については特に限定されるものではなく、水中に光触媒粒子を分散させる形態であってもよいし、光触媒粒子を固めて成形体として、当該成形体を水中に設置する形態或いは基材上に光触媒層を設けて積層体とし、当該積層体を水中に設置する形態であってもよい。 When the photocatalyst for water splitting according to the present invention is actually used for water splitting, the form of the photocatalyst is not particularly limited, and may be a form in which the photocatalyst particles are dispersed in water. The molded body may be in a form in which the molded body is placed in water or in a form in which a photocatalyst layer is provided on a substrate to form a laminated body, and the laminated body is placed in water.
以下、実施例により本発明をさらに具体的に説明するが、本発明は、その要旨を超えない限り、以下の実施例により制限されるものではない。 EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not restrict | limited by a following example, unless the summary is exceeded.
＜光触媒の結晶構造分析＞
光触媒の結晶構造については、Ｘ線回折測定装置としてリガク社製Ｒｉｎｔ−２２００を用い、ＣｕＫα（波長０．１５４１８３８ｎｍ）を線源とする粉末Ｘ線回折測定により同定した。
<Crystal structure analysis of photocatalyst>
The crystal structure of the photocatalyst was identified by powder X-ray diffraction measurement using Rint-2200 manufactured by Rigaku Corporation as an X-ray diffraction measurement apparatus and using CuKα (wavelength 0.1541838 nm) as a radiation source.
＜光触媒中の結晶相組成比（含有比）＞
混合相を有する複合酸化物におけるそれぞれの結晶相の組成比は、下記の方法により定量した。
はじめに純粋な単相結晶であるＢａＴｉ４Ｏ９、ＢａＴｉ２Ｏ５、およびＢａ４Ｔｉ１３Ｏ３０を個別に調製した後、これらサンプルのＸＲＤパターンを測定し、それぞれの特徴となるピーク （図１）のピーク強度を読み取った。
次に、前記の単相結晶ＢａＴｉ２Ｏ５およびＢａ４Ｔｉ１３Ｏ３０を、単相結晶ＢａＴｉ４Ｏ９を用いて所定の濃度に混合希釈したサンプルを数点調製した。これらのサンプルのＸＲＤパターンを測定し、各濃度における各々の結晶相のピーク強度比と濃度との相関を求めた。
そして、測定試料のＸＲＤパターンを測定し、各試料における各々の結晶相のピーク強度比を求め、前記相関から求めた検量線から組成比を算出した。
<Crystal phase composition ratio (content ratio) in the photocatalyst>
The composition ratio of each crystal phase in the composite oxide having a mixed phase was quantified by the following method.
First, pure single-phase crystals BaTi 4 O 9 , BaTi 2 O 5 , and Ba 4 Ti 13 O 30 were individually prepared, and then XRD patterns of these samples were measured, and respective characteristic peaks (FIG. 1). ) Peak intensity was read.
Next, several samples were prepared by mixing and diluting the single-phase crystals BaTi 2 O 5 and Ba 4 Ti 13 O 30 to a predetermined concentration using the single-phase crystals BaTi 4 O 9 . The XRD pattern of these samples was measured, and the correlation between the peak intensity ratio and the concentration of each crystal phase at each concentration was determined.
And the XRD pattern of the measurement sample was measured, the peak intensity ratio of each crystal phase in each sample was calculated | required, and the composition ratio was computed from the calibration curve calculated | required from the said correlation.
＜光触媒の光吸収特性の評価＞
光触媒の光吸収特性は拡散反射スペクトルの測定により観測した。測定装置としては、拡散反射ＵＶ−Ｖｉｓ吸収分光装置である日本分光社製Ｕ−ｂｅｓｔ５５０ＤＳを用いた。
<Evaluation of light absorption characteristics of photocatalyst>
The light absorption characteristics of the photocatalyst were observed by measuring the diffuse reflection spectrum. As a measurement apparatus, U-best550DS manufactured by JASCO Corporation, which is a diffuse reflection UV-Vis absorption spectrometer, was used.
＜水分解活性の評価＞
・評価装置
光水分解反応は、図２に示すような真空排気用ポンプ、循環ポンプ、光触媒懸濁液を入れる石英製内部照射型反応管（ウォータージャケットつき）、気体採取バルブおよびガスクロマトグラフ分析装置を備えた閉鎖系の反応装置で評価した。光源は４５０Ｗの高圧水銀灯（ウシオ電機社製ＵＳＨＩＯ ＵＭ−４５２）を使用し、温度上昇を避けるためランプとセルとの間のウォータージャケットに冷却水を循環させた。
<Evaluation of water splitting activity>
・ Evaluation device The photo-water splitting reaction consists of an evacuation pump, circulation pump, quartz internal irradiation reaction tube (with water jacket) containing a photocatalyst suspension, gas sampling valve and gas chromatograph analyzer as shown in FIG. Were evaluated in a closed reactor equipped with A 450 W high pressure mercury lamp (USHIO UM-452 manufactured by USHIO INC.) Was used as the light source, and cooling water was circulated in a water jacket between the lamp and the cell in order to avoid a temperature rise.
・反応条件
光触媒１．０ｇを６５０ｍｌの蒸留―イオン交換水とともにセルに入れ、１０００ｒｐｍで撹拌して均一に懸濁させた。評価の際は、あらかじめ系内を真空排気し、ガスクロマトグラフのキャリアガスであるアルゴンで系内のパージを５〜６回繰り返し、ガスクロマトグラフでの残留気体分析で酸素、窒素が検出されないことを確認し、その後に光照射を開始した。水素ガスおよび酸素ガスの生成量はガスクロマトグラフ（島津製作所製ＧＣ−８Ａ）により測定した。カラムとしてはモレキュラーシーブ５Ａ、キャリアガスとしてはアルゴンガスを用いた。
-Reaction conditions 1.0 g of photocatalyst was placed in a cell together with 650 ml of distilled-ion exchanged water and stirred uniformly at 1000 rpm to suspend it uniformly. During the evaluation, the system is evacuated in advance, and the system is purged 5-6 times with argon, the carrier gas of the gas chromatograph, and it is confirmed that oxygen and nitrogen are not detected by residual gas analysis in the gas chromatograph. Then, light irradiation was started. The production amounts of hydrogen gas and oxygen gas were measured by a gas chromatograph (GC-8A manufactured by Shimadzu Corporation). Molecular sieve 5A was used as the column, and argon gas was used as the carrier gas.
＜水分解用光触媒の調製＞
光触媒の調製には以下の試薬を使用した。
炭酸バリウム ＢａＣＯ３（和光純薬工業株式会社社製 純度９９．９％）
二酸化チタン ＴｉＯ２ （日本アエロジル社製、純度９９．５％）
チタンテトライソプロポキシド Ｔｉ［（ＣＨ３）２ＣＨＯ］４（和光純薬工業株式会社社製 純度９５．０％）
エチレングリコール （和光純薬工業株式会社社製 純度９９．５％）
無水クエン酸 （和光純薬工業株式会社製、９８．０％)
硝酸ニッケル６水和物 Ｎｉ（ＮＯ３）３・６Ｈ２Ｏ（和光純薬工業株式会社製 純度９９．９％）
塩化ロジウム３水和物 ＲｈＣｌ３・３Ｈ２Ｏ（和光純薬工業株式会社製 純度９９．０％）
硝酸クロム９水和物 Ｃｒ（ＮＯ３）３・９Ｈ２Ｏ（和光純薬工業株式会社製 純度９９．９％）
<Preparation of photocatalyst for water splitting>
The following reagents were used for the preparation of the photocatalyst.
Barium carbonate BaCO 3 (Wako Pure Chemical Industries, Ltd., purity 99.9%)
Titanium dioxide TiO 2 (manufactured by Nippon Aerosil Co., Ltd., purity 99.5%)
Titanium tetraisopropoxide Ti [(CH 3 ) 2 CHO] 4 (Wako Pure Chemical Industries, Ltd., purity 95.0%)
Ethylene glycol (Pure 99.5%, manufactured by Wako Pure Chemical Industries, Ltd.)
Citric anhydride (Wako Pure Chemical Industries, 98.0%)
Nickel nitrate hexahydrate Ni (NO 3) 3 · 6H 2 O ( Wako Pure Chemical Industries, Ltd. purity: 99.9%)
Rhodium trihydrate RhCl 3 · 3H 2 O chloride (produced by Wako Pure Chemical Industries, Ltd. purity 99.0%)
Chromium nitrate nonahydrate Cr (NO 3) 3 · 9H 2 O ( Wako Pure Chemical Industries, Ltd. purity: 99.9%)
（実施例１）
・錯体重合法によるポリマー錯体の調製
３００ｍｌビーカーに入れたエチレングリコール３８．５ｇ中に、チタンテトライソプロポキシドを１８．４６ｇ加えた後、８０℃で、撹拌子の回転数を３５０ｒｐｍに設定したスターラーで攪拌させ、無水クエン酸２７．５ｇを加えた。無水クエン酸が完全に溶解した後、さらに炭酸バリウム３．９４ｇを加え、均一な溶液とした。撹拌子の回転数を３５０ｒｐｍに保ったまま、この溶液の温度を１８５℃として２時間重合させ、Ｂａ／Ｔｉポリマー錯体（Ｂａ：Ｔｉ＝４：１３（モル比））とした。
Example 1
・ Preparation of polymer complex by complex polymerization method After adding 18.46 g of titanium tetraisopropoxide to 38.5 g of ethylene glycol in a 300 ml beaker, the stirrer was set at 80 ° C. and the rotation speed of the stirrer was set to 350 rpm. And 27.5 g of anhydrous citric acid was added. After the anhydrous citric acid was completely dissolved, 3.94 g of barium carbonate was further added to obtain a uniform solution. While maintaining the rotation speed of the stirrer at 350 rpm, the temperature of this solution was set at 185 ° C. for polymerization for 2 hours to obtain a Ba / Ti polymer complex (Ba: Ti = 4: 13 (molar ratio)).
・ポリマー錯体の熱分解による前駆体の調製
前述の通り重合させた後、撹拌子の回転数を３５０ｒｐｍに保ったまま、ビーカーの温度を１８５℃から３５０℃に上昇させ１５分間熱分解を行った。さらにビーカーを円筒状電気炉にうつし、３５０℃でさらに継続して１８時間熱分解を行って前駆体を得た。その後、得られたビーカー内の前駆体を３５０℃に加熱を続けながらガラス棒で粉砕した。粉砕後、ビーカーを室温に戻し、粉砕した前駆体の粉末をメノウ乳鉢にうつして１０〜３０マイクロメートル程度の粒子となるまで粉砕した。
Preparation of precursor by thermal decomposition of polymer complex After polymerization as described above, the temperature of the beaker was increased from 185 ° C. to 350 ° C. and the thermal decomposition was performed for 15 minutes while maintaining the rotation speed of the stirrer at 350 rpm. . Further, the beaker was transferred to a cylindrical electric furnace, and further thermally decomposed at 350 ° C. for 18 hours to obtain a precursor. Thereafter, the precursor in the obtained beaker was pulverized with a glass rod while continuing to be heated to 350 ° C. After pulverization, the beaker was returned to room temperature, and the pulverized precursor powder was transferred to an agate mortar and pulverized until particles of about 10 to 30 micrometers were obtained.
・複合酸化物の調製
得られた前駆体を、アルミナ坩堝にうつし、電気炉を使用して８００℃で２０時間焼成し複合酸化物を得た。得られた複合酸化物はメノウ乳鉢で０．１〜０．５マイクロメートル程度の粒子となるまで粉砕した。
得られた複合酸化物の組成比を表２に示す。また、得られた複合酸化物の拡散反射スペクトルを測定した。結果を図３に示す。
-Preparation of composite oxide The obtained precursor was transferred to an alumina crucible and fired at 800 ° C for 20 hours using an electric furnace to obtain a composite oxide. The obtained composite oxide was pulverized in an agate mortar until it became particles of about 0.1 to 0.5 micrometers.
Table 2 shows the composition ratio of the obtained composite oxide. Moreover, the diffuse reflection spectrum of the obtained composite oxide was measured. The results are shown in FIG.
・助触媒の担持
粉砕した複合酸化物１．２ｇに、硝酸ニッケル・６水和物０．０２３４５ｇ（ＮｉＯとして０．５重量％）を、水を溶媒として含浸担持し、ロータリーエバポレーターを用いて蒸発乾固した。これを引き続き２７０℃で１時間焼成し、複合酸化物にＮｉＯを担持した。担持したＮｉＯを助触媒として活性化させるため、前処理を下記の条件により行った。まず、閉鎖循環系にて、４５０℃で３００Ｔｏｒｒの水素雰囲気下、２時間水素還元を行った。その後４５０℃で水素を排気後、２００℃まで降温し、酸素を導入した後、引き続き２００℃、１５０Ｔｏｒｒの酸素雰囲気下で１時間酸素再酸化を行った。
・ Supporting promoter
1.2 g of the ground composite oxide was impregnated with 0.02345 g of nickel nitrate hexahydrate (0.5 wt% as NiO) using water as a solvent, and evaporated to dryness using a rotary evaporator. This was subsequently fired at 270 ° C. for 1 hour, and NiO was supported on the composite oxide. In order to activate the supported NiO as a promoter, pretreatment was performed under the following conditions. First, hydrogen reduction was performed in a closed circulation system at 450 ° C. in a 300 Torr hydrogen atmosphere for 2 hours. Then, after evacuating hydrogen at 450 ° C., the temperature was lowered to 200 ° C., oxygen was introduced, and then oxygen reoxidation was continued for 1 hour in an oxygen atmosphere at 200 ° C. and 150 Torr.
以上の手順を経て、実施例１に係る水分解用光触媒を得た。得られた水分解用光触媒を用いて上記記載の方法によって光水分解反応を行い、水分解活性を評価した。結果を表２に示す。 Through the above procedure, the photocatalyst for water splitting according to Example 1 was obtained. Using the obtained water-splitting photocatalyst, a photo-water-splitting reaction was performed by the method described above, and water-splitting activity was evaluated. The results are shown in Table 2.
（実施例２）
実施例１に記載の複合酸化物１．２ｇに、塩化ロジウム・３水和物０．００３０７４ｇ（３．０７ｍｇ）（Ｒｈとして０．１重量％）、硝酸クロム・９水和物０．００９２４４ｇ（Ｃｒとして０．１重量％）を、水を溶媒として含浸担持し、ロータリーエバポレーターを用いて蒸発乾固した。これを引き続き３５０℃で２時間焼成することによって複合酸化物にＲｈ−Ｃｒ複合酸化物を担持し、実施例２に係る水分解用光触媒を得た。この光触媒を用いて上記記載の方法によって光水分解反応を行い、水分解活性を評価した。結果を表２に示す。
(Example 2)
To 1.2 g of the composite oxide described in Example 1, 0.003074 g (3.07 mg) of rhodium chloride trihydrate (0.1 wt% as Rh), 0.009224 g of chromium nitrate nonahydrate ( 0.1 wt% as Cr) was impregnated and supported using water as a solvent, and evaporated to dryness using a rotary evaporator. This was subsequently fired at 350 ° C. for 2 hours to carry the Rh—Cr composite oxide on the composite oxide, and the photocatalyst for water splitting according to Example 2 was obtained. Using this photocatalyst, the water splitting reaction was carried out by the method described above, and the water splitting activity was evaluated. The results are shown in Table 2.
（実施例３）
チタンテトライソプロポキシド１９．３０ｇ、炭酸バリウム３．９４４ｇを用いた以外は、実施例１と同様の操作を行い複合酸化物（Ｂａ：Ｔｉ＝４：１４（モル比））を得た。得られた複合酸化物の組成を表２に示す。
(Example 3)
A composite oxide (Ba: Ti = 4: 14 (molar ratio)) was obtained in the same manner as in Example 1 except that 19.30 g of titanium tetraisopropoxide and 3.944 g of barium carbonate were used. Table 2 shows the composition of the obtained composite oxide.
その後、実施例２に記載した手順と同様にして複合酸化物にＲｈ−Ｃｒ複合酸化物を担持し、実施例３に係る水分解用光触媒を得た。この光触媒を用いて上記記載の方法によって光水分解反応を行い、水分解活性を評価した。結果を表２に示す。 Thereafter, the Rh—Cr composite oxide was supported on the composite oxide in the same manner as described in Example 2 to obtain a water splitting photocatalyst according to Example 3. Using this photocatalyst, the water splitting reaction was carried out by the method described above, and the water splitting activity was evaluated. The results are shown in Table 2.
（実施例４）
・固相法による複合酸化物の調製
炭酸バリウム０．４９９６ｇと二酸化チタン０．７０７８ｇを、粉砕混合し、１０００℃で２０時間焼成し、複合酸化物（Ｂａ：Ｔｉ＝４：１４（モル比））を調製した。得られた複合酸化物の組成を表２に示す。
Example 4
Preparation of complex oxide by solid phase method 0.4996 g of barium carbonate and 0.7078 g of titanium dioxide were pulverized and mixed and baked at 1000 ° C. for 20 hours to obtain a complex oxide (Ba: Ti = 4: 14 (molar ratio)). ) Was prepared. Table 2 shows the composition of the obtained composite oxide.
・助触媒の担持
粉砕した複合酸化物１．２ｇに、塩化ロジウム・３水和物０．００３０７４ｇ（Ｒｈとして０．１重量％）、硝酸クロム・９水和物０．００９２４４ｇ（Ｃｒとして０．１重量％）を、水を溶媒として含浸担持し、ロータリーエバポレーターを用いて蒸発乾固した。引き続き３５０℃で２時間焼成し、複合酸化物にＲｈ−Ｃｒ複合酸化物を担持し、実施例４に係る水分解用光触媒を得た。この光触媒を用いて上記記載の方法によって光水分解反応を行い、水分解活性を評価した。結果を表２に示す。
Co-catalyst loading To 1.2 g of the pulverized composite oxide, 0.003074 g of rhodium chloride trihydrate (0.1% by weight as Rh) and 0.009244 g of chromium nitrate nonahydrate (0. 1% by weight) was impregnated with water as a solvent, and evaporated to dryness using a rotary evaporator. Subsequently, the mixture was baked at 350 ° C. for 2 hours, and the Rh—Cr composite oxide was supported on the composite oxide to obtain a water splitting photocatalyst according to Example 4. Using this photocatalyst, the water splitting reaction was carried out by the method described above, and the water splitting activity was evaluated. The results are shown in Table 2.
（実施例５）
焼成温度を９００℃とした以外は、実施例４と同様に調製し、複合酸化物を得た後、Ｒｈ−Ｃｒ複合酸化物を担持して実施例５に係る水分解用光触媒を得た。この光触媒を用いて上記記載の方法によって光水分解反応を行い、水分解活性を評価した。得られた複合酸化物の組成や、得られた水分解用光触媒の水分解活性を表２に示す。
(Example 5)
Except that the calcination temperature was 900 ° C., it was prepared in the same manner as in Example 4 to obtain a composite oxide, and then the Rh—Cr composite oxide was supported to obtain the water splitting photocatalyst according to Example 5. Using this photocatalyst, the water splitting reaction was carried out by the method described above, and the water splitting activity was evaluated. Table 2 shows the composition of the obtained composite oxide and the water splitting activity of the obtained water splitting photocatalyst.
（実施例６）
焼成温度を９５０℃とした以外は、実施例４と同様に調製し、複合酸化物を得た後、Ｒｈ−Ｃｒ複合酸化物を担持して実施例６に係る水分解用光触媒を得た。この光触媒を用いて上記記載の方法によって光水分解反応を行い、水分解活性を評価した。得られた複合酸化物の組成や、得られた水分解用光触媒の水分解活性を表２に示す。
(Example 6)
Except that the calcination temperature was 950 ° C., it was prepared in the same manner as in Example 4 to obtain a composite oxide, and then a Rh—Cr composite oxide was supported to obtain a water splitting photocatalyst according to Example 6. Using this photocatalyst, the water splitting reaction was carried out by the method described above, and the water splitting activity was evaluated. Table 2 shows the composition of the obtained composite oxide and the water splitting activity of the obtained water splitting photocatalyst.
（実施例７）
焼成温度を１０５０℃とした以外は、実施例４と同様に調製し、複合酸化物を得た後、Ｒｈ−Ｃｒ複合酸化物を担持して実施例７に係る水分解用光触媒を得た。この光触媒を用いて上記記載の方法によって光水分解反応を行い、水分解活性を評価した。得られた複合酸化物の組成や、得られた水分解用光触媒の水分解活性を表２に示す。
(Example 7)
Except that the calcination temperature was 1050 ° C., it was prepared in the same manner as in Example 4 to obtain a composite oxide, and then the Rh—Cr composite oxide was supported to obtain the water splitting photocatalyst according to Example 7. Using this photocatalyst, the water splitting reaction was carried out by the method described above, and the water splitting activity was evaluated. Table 2 shows the composition of the obtained composite oxide and the water splitting activity of the obtained water splitting photocatalyst.
（実施例８）
焼成温度を１１００℃とした以外は、実施例４と同様に調製し、複合酸化物を得た後、Ｒｈ−Ｃｒ複合酸化物を担持して実施例８に係る水分解用光触媒を得た。この光触媒を用いて上記記載の方法によって光水分解反応を行い、水分解活性を評価した。得られた複合酸化物の組成や、得られた水分解用光触媒の水分解活性を表２に示す。
(Example 8)
Except that the calcining temperature was 1100 ° C., it was prepared in the same manner as in Example 4 to obtain a composite oxide, and then the Rh—Cr composite oxide was supported to obtain the water splitting photocatalyst according to Example 8. Using this photocatalyst, the water splitting reaction was carried out by the method described above, and the water splitting activity was evaluated. Table 2 shows the composition of the obtained composite oxide and the water splitting activity of the obtained water splitting photocatalyst.
（比較例１）
チタンテトライソプロポキシドを２２．７４ｇ、炭酸バリウムを３．９４ｇ使用し、Ｂａ：Ｔｉ＝１：４とした以外は、実施例１と同様の操作を行い、チタン酸バリウム（ＢａＴｉ４Ｏ９）の単相結晶を得た。引き続き、実施例１と同様の操作を行い、ＢａＴｉ４Ｏ９にＮｉＯを担持し、比較例１に係る水分解用光触媒を得た。得られた光触媒を用いて上記の方法によって光水分解反応を行い、水分解活性を評価した。結果を表２に示す。
(Comparative Example 1)
Barium titanate (BaTi 4 O 9 ) was used in the same manner as in Example 1 except that 22.74 g of titanium tetraisopropoxide and 3.94 g of barium carbonate were used and Ba: Ti = 1: 4. A single phase crystal was obtained. Subsequently, the same operation as in Example 1 was performed, and NiO was supported on BaTi 4 O 9 to obtain a water splitting photocatalyst according to Comparative Example 1. Using the obtained photocatalyst, the water-splitting reaction was carried out by the above method, and the water-splitting activity was evaluated. The results are shown in Table 2.
（比較例２）
チタンテトライソプロポキシドを１１．３７ｇ、炭酸バリウムを３．９４ｇ使用し、Ｂａ：Ｔｉ＝１：２とした以外は、実施例１と同様の操作を行い、チタン酸バリウム（ＢａＴｉ２Ｏ５）の単相結晶を得た。引き続き、実施例１と同様の操作を行い、ＢａＴｉ２Ｏ５にＮｉＯを担持し、比較例２に係る水分解用光触媒を得た。得られた光触媒を用いて上記の方法によって光水分解反応を行い、水分解活性を評価した。結果を表２に示す。
(Comparative Example 2)
Barium titanate (BaTi 2 O 5 ) was prepared in the same manner as in Example 1 except that 11.37 g of titanium tetraisopropoxide and 3.94 g of barium carbonate were used and Ba: Ti = 1: 2. A single phase crystal was obtained. Subsequently, the same operation as in Example 1 was performed, and NiO was supported on BaTi 2 O 5 to obtain a water splitting photocatalyst according to Comparative Example 2. Using the obtained photocatalyst, the water-splitting reaction was carried out by the above method, and the water-splitting activity was evaluated. The results are shown in Table 2.
（比較例３）
チタンテトライソプロポキシドを１４．２１ｇ、炭酸バリウムを３．９４ｇ使用し、Ｂａ：Ｔｉ＝２：５とした以外は、実施例１と同様の操作を行い、複合酸化物を得た。得られた複合酸化物の組成を表２に示す。
引き続き、実施例１と同様の操作により複合酸化物にＮｉＯを担持し、比較例３に係る水分解用光触媒を得た。得られた光触媒を用いて上記の方法によって光水分解反応を行い、水分解活性を評価した。結果を表２に示す。
(Comparative Example 3)
A composite oxide was obtained in the same manner as in Example 1 except that 14.21 g of titanium tetraisopropoxide and 3.94 g of barium carbonate were used and Ba: Ti = 2: 5 was used. Table 2 shows the composition of the obtained composite oxide.
Subsequently, NiO was supported on the composite oxide in the same manner as in Example 1 to obtain a water splitting photocatalyst according to Comparative Example 3. Using the obtained photocatalyst, the water-splitting reaction was carried out by the above method, and the water-splitting activity was evaluated. The results are shown in Table 2.
（比較例４）
チタンテトライソプロポキシドを２８．４２ｇ、炭酸バリウムを３．９４ｇ使用し、Ｂａ：Ｔｉ＝１：５とした以外は、実施例１と同様の操作を行い、チタン酸バリウム（ＢａＴｉ５Ｏ１１）の単相結晶を得た。引き続き、実施例１と同様の操作を行い、ＢａＴｉ５Ｏ１１にＮｉＯを担持し、比較例４に係る水分解用光触媒を得た。得られた光触媒を用いて上記の方法によって光水分解反応を行い、水分解活性を評価した。結果を表２に示す。
(Comparative Example 4)
Barium titanate (BaTi 5 O 11 ) was prepared in the same manner as in Example 1 except that 28.42 g of titanium tetraisopropoxide and 3.94 g of barium carbonate were used and Ba: Ti = 1: 5. A single phase crystal was obtained. Subsequently, the same operation as in Example 1 was performed, and NiO was supported on BaTi 5 O 11 to obtain a water splitting photocatalyst according to Comparative Example 4. Using the obtained photocatalyst, the water-splitting reaction was carried out by the above method, and the water-splitting activity was evaluated. The results are shown in Table 2.
（比較例５）
チタンテトライソプロポキシドを２５．５８ｇ、炭酸バリウムを３．９４ｇ使用し、Ｂａ：Ｔｉ＝２：９とした以外は、実施例１と同様の操作を行い、複合酸化物を得た。得られた複合酸化物の組成を表２に示す。
引き続き、実施例１と同様の操作により複合酸化物にＮｉＯを担持し、比較例５に係る水分解用光触媒を得た。得られた光触媒を用いて上記の方法によって光水分解反応を行い、水分解活性を評価した。結果を表２に示す。
(Comparative Example 5)
A composite oxide was obtained in the same manner as in Example 1 except that 25.58 g of titanium tetraisopropoxide and 3.94 g of barium carbonate were used and Ba: Ti = 2: 9. Table 2 shows the composition of the obtained composite oxide.
Subsequently, NiO was supported on the composite oxide by the same operation as in Example 1 to obtain a water splitting photocatalyst according to Comparative Example 5. Using the obtained photocatalyst, the water-splitting reaction was carried out by the above method, and the water-splitting activity was evaluated. The results are shown in Table 2.
（比較例６）
チタンテトライソプロポキシドを２１．３０ｇ、炭酸バリウムを３．９４ｇ使用し、Ｂａ：Ｔｉ＝４：１５とした以外は、実施例１と同様の操作を行い、複合酸化物を得た。得られた複合酸化物の組成を表２に示す。
引き続き、実施例１と同様の操作により複合酸化物にＮｉＯを担持し、比較例６に係る水分解用光触媒を得た。得られた光触媒を用いて上記の方法によって光水分解反応を行い、水分解活性を評価した。結果を表２に示す。
(Comparative Example 6)
A composite oxide was obtained in the same manner as in Example 1 except that 21.30 g of titanium tetraisopropoxide and 3.94 g of barium carbonate were used and Ba: Ti = 4: 15. Table 2 shows the composition of the obtained composite oxide.
Subsequently, NiO was supported on the composite oxide by the same operation as in Example 1 to obtain a water splitting photocatalyst according to Comparative Example 6. Using the obtained photocatalyst, the water-splitting reaction was carried out by the above method, and the water-splitting activity was evaluated. The results are shown in Table 2.
（比較例７）
比較例１で得られたチタン酸バリウム（ＢａＴｉ４Ｏ９）に、実施例２に記載の担持方法と同様の操作により、Ｒｈ−Ｃｒ複合酸化物を担持し、比較例７に係る水分解用光触媒を得た。得られた光触媒を用いて上記の方法によって光水分解反応を行い、水分解活性を評価した。結果を表２に示す。
(Comparative Example 7)
The barium titanate (BaTi 4 O 9 ) obtained in Comparative Example 1 was loaded with Rh—Cr composite oxide by the same operation as the loading method described in Example 2, and the water splitting according to Comparative Example 7 was performed. A photocatalyst was obtained. Using the obtained photocatalyst, the water-splitting reaction was carried out by the above method, and the water-splitting activity was evaluated. The results are shown in Table 2.
（比較例８）
比較例２で得られたチタン酸バリウム（ＢａＴｉ２Ｏ５）に、実施例２に記載の担持方法と同様の操作により、Ｒｈ−Ｃｒ複合酸化物を担持し、比較例８に係る水分解用光触媒を得た。得られた光触媒を用いて上記の方法によって光水分解反応を行い、水分解活性を評価した。結果を表２に示す。
(Comparative Example 8)
The barium titanate (BaTi 2 O 5 ) obtained in Comparative Example 2 was loaded with Rh—Cr composite oxide by the same operation as the loading method described in Example 2, and the water splitting according to Comparative Example 8 was performed. A photocatalyst was obtained. Using the obtained photocatalyst, the water-splitting reaction was carried out by the above method, and the water-splitting activity was evaluated. The results are shown in Table 2.
（比較例９）
前駆体の焼成を１０００℃、２０時間としたほかは実施例１と同様の操作によりチタン酸バリウム（Ｂａ４Ｔｉ１３Ｏ３０）を得た。得られたチタン酸バリウム（Ｂａ４Ｔｉ１３Ｏ３０）に、実施例２に記載の担持方法と同様の操作により、Ｒｈ−Ｃｒ複合酸化物を担持し、比較例８に係る水分解用光触媒を得た。得られた光触媒を用いて上記の方法によって光水分解反応を行い、水分解活性を評価した。結果を表２に示す。
(Comparative Example 9)
Barium titanate (Ba 4 Ti 13 O 30 ) was obtained in the same manner as in Example 1 except that the precursor was baked at 1000 ° C. for 20 hours. The obtained barium titanate (Ba 4 Ti 13 O 30 ) was loaded with a Rh—Cr composite oxide by the same operation as the loading method described in Example 2, and the photocatalyst for water splitting according to Comparative Example 8 was used. Obtained. Using the obtained photocatalyst, the water-splitting reaction was carried out by the above method, and the water-splitting activity was evaluated. The results are shown in Table 2.
（比較例１０）
焼成温度を９５０℃として調製した以外は、実施例３と同様の操作により複合酸化物を得た。得られた複合酸化物の組成を表２に示す。
引き続き、実施例２と同様の操作により複合酸化物に、Ｒｈ−Ｃｒ複合酸化物を担持し、比較例１０に係る水分解用光触媒を得た。得られた光触媒を用いて上記の方法によって光水分解反応を行い、水分解活性を評価した。結果を表２に示す。
(Comparative Example 10)
A composite oxide was obtained by the same operation as in Example 3, except that the firing temperature was 950 ° C. Table 2 shows the composition of the obtained composite oxide.
Subsequently, the Rh—Cr composite oxide was supported on the composite oxide in the same manner as in Example 2 to obtain a water splitting photocatalyst according to Comparative Example 10. Using the obtained photocatalyst, the water-splitting reaction was carried out by the above method, and the water-splitting activity was evaluated. The results are shown in Table 2.
＜考察＞
単相チタン酸バリウムの光触媒水分解活性は、ＢａＴｉ４Ｏ９がもっとも大きいことは既に知られている（Yamashita, Y.; Tada, M.; Kakihana, M.; Osada, M.; Yoshida, K., J. Mater. Chem. 2002, 12 (6), 1782-1786. および Kohno, M.; Kaneko, T.; Ogura, S.; Sato, K.; Yasunobu Inoue, J. Chem. Soc., Faraday Trans. 1998, 94 (1), 89-94.)。
<Discussion>
It is already known that BaTi 4 O 9 has the largest photocatalytic water splitting activity of single-phase barium titanate (Yamashita, Y .; Tada, M .; Kakihana, M .; Osada, M .; Yoshida, K ., J. Mater. Chem. 2002, 12 (6), 1782-1786. And Kohno, M .; Kaneko, T .; Ogura, S .; Sato, K .; Yasunobu Inoue, J. Chem. Soc., Faraday Trans. 1998, 94 (1), 89-94.).
一方、表２に示すとおり、３＜Ｔｉ／Ｂａ＜４の範囲で調製し、含有相としてＢａＴｉ４Ｏ９結晶相を６０％以上含有し、その他の結晶相としてＢａＴｉ２Ｏ５結晶相を含んでいる実施例１は、低活性なＢａＴｉ２Ｏ５で希釈されているにもかかわらず、もっとも高活性な光触媒として知られるＢａＴｉ４Ｏ９或いは公知物質であるＢａＴｉ２Ｏ５にＮｉＯを担持した比較例１、比較例２に比べて高い活性を示した。また、助触媒を変更した実施例２は、同じく助触媒を変更した比較例７や比較例８に比べて高い活性を示した。
このことから、３＜Ｔｉ／Ｂａ＜４の範囲で、且つ、２つ以上の結晶相が共存する混合組成とすることが重要であることが明らかとなった。
On the other hand, as shown in Table 2, prepared in the range of 3 <Ti / Ba <4, containing 60% or more of BaTi 4 O 9 crystal phase as the contained phase, and containing BaTi 2 O 5 crystal phase as the other crystal phase example 1 you are in, despite being diluted with a low active BaTi 2 O 5, was supported NiO to BaTi 2 O 5 is BaTi 4 O 9 or known substances, known as the most highly active photocatalyst Compared with Comparative Example 1 and Comparative Example 2, the activity was high. Moreover, Example 2 which changed the promoter showed high activity compared with the comparative example 7 and the comparative example 8 which also changed the promoter.
From this, it became clear that it is important to have a mixed composition in the range of 3 <Ti / Ba <4 and in which two or more crystal phases coexist.
さらに、錯体重合法で調製した実施例３や固相法で調製した実施例４〜７のいずれについても、比較例７よりも高活性であったことから、３＜Ｔｉ／Ｂａ＜４の範囲であり、かつ、ＢａＴｉ４Ｏ９の含有量が６０％以上であれば、前駆体および焼成温度などの調製法によらず高活性な光触媒が得られることが明らかとなった。 Furthermore, since both Example 3 prepared by the complex polymerization method and Examples 4 to 7 prepared by the solid phase method were more active than Comparative Example 7, the range of 3 <Ti / Ba <4. In addition, when the content of BaTi 4 O 9 is 60% or more, it became clear that a highly active photocatalyst can be obtained regardless of the preparation method such as the precursor and the firing temperature.
一方、複合酸化物が混合相を有するものであっても、Ｔｉ／Ｂａ＜３である比較例３や４＜Ｔｉ／Ｂａである比較例５では、比較例１に比べて活性が低くなっており、このことから光触媒のモル比（Ｔｉ／Ｂａ）が３＜Ｔｉ／Ｂａ＜４の範囲であることが重要であることが明らかとなった。 On the other hand, even if the composite oxide has a mixed phase, the activity is lower in Comparative Example 3 where Ti / Ba <3 and Comparative Example 5 where 4 <Ti / Ba than Comparative Example 1. From this, it was revealed that the molar ratio of the photocatalyst (Ti / Ba) is in the range of 3 <Ti / Ba <4.
また、比較例６或いは比較例１０は、モル比（Ｔｉ／Ｂａ）が３＜Ｔｉ／Ｂａ＜４の範囲に入ってはいるものの、混合相中にＢａＴｉ２Ｏ５を含まないため、それぞれ比較例１或いは比較例７に比べて活性が著しく低くなっており、このことから、混合相中にはＢａＴｉ２Ｏ５が含まれる必要があることが明らかとなった。 In Comparative Example 6 or Comparative Example 10, although the molar ratio (Ti / Ba) is in the range of 3 <Ti / Ba <4, the mixed phase does not contain BaTi 2 O 5, and thus the comparison is made. The activity was remarkably lower than that of Example 1 or Comparative Example 7, and this revealed that the mixed phase must contain BaTi 2 O 5 .
さらに、実施例７、８のように、ＢａＴｉ４Ｏ９結晶相とＢａＴｉ２Ｏ５結晶相とＢａ４Ｔｉ１３Ｏ３０結晶相とを含む複合酸化物において、ＢａＴｉ４Ｏ９結晶相ではなくＢａ４Ｔｉ１３Ｏ３０結晶相が主相となる場合にも、比較的大きな活性を示した。 Further, as in Examples 7 and 8, in the composite oxide including the BaTi 4 O 9 crystal phase, the BaTi 2 O 5 crystal phase, and the Ba 4 Ti 13 O 30 crystal phase, the BaTi 4 O 9 crystal phase is used instead of the BaTi 4 O 9 crystal phase. Even when the 4 Ti 13 O 30 crystal phase became the main phase, a relatively large activity was exhibited.
以上のことから、チタンおよびバリウムを含む複合酸化物と助触媒とを含有する水分解用光触媒の水分解活性を向上させるためには、複合酸化物において、
（１）ＢａＴｉ４Ｏ９結晶相とＢａＴｉ２Ｏ５結晶相とが含まれるものとし、ＢａＴｉ４Ｏ９結晶相とＢａＴｉ２Ｏ５結晶相との合計を１００モル％とした場合において、ＢａＴｉ４Ｏ９結晶相の含有比が６０モル％以上であり、かつ、バリウム原子に対するチタン原子のモル比（Ｔｉ／Ｂａ）が３＜Ｔｉ／Ｂａ＜４であるものとするか、
（２）ＢａＴｉ４Ｏ９結晶相とＢａＴｉ２Ｏ５結晶相とＢａ４Ｔｉ１３Ｏ３０結晶相とが含まれるものとし、ＢａＴｉ４Ｏ９結晶相とＢａＴｉ２Ｏ５結晶相とＢａ４Ｔｉ１３Ｏ３０結晶相との合計を１００モル％とした場合において、ＢａＴｉ４Ｏ９結晶相またはＢａ４Ｔｉ１３Ｏ３０結晶相の含有比が６０モル％以上であり、かつ、バリウム原子に対するチタン原子のモル比（Ｔｉ／Ｂａ）が３＜Ｔｉ／Ｂａ＜４であるものとする
ことが有効であることが明らかとなった。
From the above, in order to improve the water splitting activity of the photocatalyst for water splitting containing the composite oxide containing titanium and barium and the promoter, in the composite oxide,
(1) In the case where the BaTi 4 O 9 crystal phase and the BaTi 2 O 5 crystal phase are included, and the total of the BaTi 4 O 9 crystal phase and the BaTi 2 O 5 crystal phase is 100 mol%, the BaTi 4 Whether the content ratio of the O 9 crystal phase is 60 mol% or more and the molar ratio of titanium atoms to barium atoms (Ti / Ba) is 3 <Ti / Ba <4,
(2) A BaTi 4 O 9 crystal phase, a BaTi 2 O 5 crystal phase and a Ba 4 Ti 13 O 30 crystal phase are included, and a BaTi 4 O 9 crystal phase, a BaTi 2 O 5 crystal phase and a Ba 4 Ti 13 crystal are included. When the total amount with respect to the O 30 crystal phase is 100 mol%, the content ratio of the BaTi 4 O 9 crystal phase or the Ba 4 Ti 13 O 30 crystal phase is 60 mol% or more, and the titanium atoms have a barium atom content. It has been found that it is effective that the molar ratio (Ti / Ba) is 3 <Ti / Ba <4.
以上、現時点において、もっとも、実践的であり、かつ、好ましいと思われる実施形態に関連して本発明を説明したが、本発明は、本願明細書中に開示された実施形態に限定されるものではなく、請求の範囲および明細書全体から読み取れる発明の要旨或いは思想に反しない範囲で適宜変更可能であり、そのような変更を伴う水分解用光触媒もまた本発明の技術的範囲に包含されるものとして理解されなければならない。 While the present invention has been described in connection with embodiments that are presently the most practical and preferred, the present invention is not limited to the embodiments disclosed herein. However, the invention can be changed as appropriate without departing from the scope or spirit of the invention that can be read from the claims and the entire specification, and a water-catalyzed photocatalyst accompanying such a change is also included in the technical scope of the present invention. It must be understood as a thing.
本発明に係る光触媒は、従来のチタン酸バリウム系光触媒と比べて高い水分解活性を有し、太陽光を利用した水分解反応を行うことにより水素および／または酸素を製造する光水分解反応に特に好適に用いられる。 The photocatalyst according to the present invention has a high water splitting activity as compared with conventional barium titanate photocatalysts, and is used for a photohydrolysis reaction that produces hydrogen and / or oxygen by performing a water splitting reaction using sunlight. Particularly preferably used.
Claims (6)
前記複合酸化物は、
ＢａＴｉ４Ｏ９結晶相とＢａＴｉ２Ｏ５結晶相とを含み、
前記ＢａＴｉ ２ Ｏ ５ 結晶相の含有比が１０モル％以上であり、
前記ＢａＴｉ４Ｏ９結晶相と前記ＢａＴｉ２Ｏ５結晶相との合計を１００モル％とした場合において、前記ＢａＴｉ４Ｏ９結晶相の含有比が６０モル％以上であり、かつ、
バリウム原子に対するチタン原子のモル比（Ｔｉ／Ｂａ）が３＜Ｔｉ／Ｂａ＜４である、
水分解用光触媒。 A photocatalyst for water splitting comprising a composite oxide containing titanium and barium and a promoter,
The composite oxide is
A BaTi 4 O 9 crystal phase and a BaTi 2 O 5 crystal phase,
The content ratio of the BaTi 2 O 5 crystal phase is 10 mol% or more,
When the total of the BaTi 4 O 9 crystal phase and the BaTi 2 O 5 crystal phase is 100 mol%, the content ratio of the BaTi 4 O 9 crystal phase is 60 mol% or more, and
The molar ratio of titanium atoms to barium atoms (Ti / Ba) is 3 <Ti / Ba <4.
Photocatalyst for water splitting.
前記複合酸化物は、
ＢａＴｉ４Ｏ９結晶相とＢａＴｉ２Ｏ５結晶相とＢａ４Ｔｉ１３Ｏ３０結晶相とを含み、
前記ＢａＴｉ ２ Ｏ ５ 結晶相の含有比が１０モル％以上であり、
前記ＢａＴｉ４Ｏ９結晶相と前記ＢａＴｉ２Ｏ５結晶相と前記Ｂａ４Ｔｉ１３Ｏ３０結晶相との合計を１００モル％とした場合において、前記ＢａＴｉ４Ｏ９結晶相または前記Ｂａ４Ｔｉ１３Ｏ３０結晶相の含有比が６０モル％以上であり、かつ、
バリウム原子に対するチタン原子のモル比（Ｔｉ／Ｂａ）が３＜Ｔｉ／Ｂａ＜４である、
水分解用光触媒。 A photocatalyst for water splitting comprising a composite oxide containing titanium and barium and a promoter,
The composite oxide is
A BaTi 4 O 9 crystal phase, a BaTi 2 O 5 crystal phase and a Ba 4 Ti 13 O 30 crystal phase,
The content ratio of the BaTi 2 O 5 crystal phase is 10 mol% or more,
When the sum of the BaTi 4 O 9 crystal phase, the BaTi 2 O 5 crystal phase, and the Ba 4 Ti 13 O 30 crystal phase is 100 mol%, the BaTi 4 O 9 crystal phase or the Ba 4 Ti 13 The content ratio of the O 30 crystal phase is 60 mol% or more, and
The molar ratio of titanium atoms to barium atoms (Ti / Ba) is 3 <Ti / Ba <4.
Photocatalyst for water splitting.
請求項１または２に記載の水分解用光触媒。 The content ratio of the BaTi 2 O 5 crystal phase is 35 mol% or less ,
The photocatalyst for water splitting according to claim 1 or 2.
請求項１〜３のいずれか１項に記載の水分解用光触媒。 The promoter is at least one selected from Ni oxide and Rh—Cr composite oxide,
The photocatalyst for water splitting according to any one of claims 1 to 3.
チタン原子を含む原料とバリウム原子を含む原料とを、バリウム原子に対するチタン原子のモル比（Ｔｉ／Ｂａ）が３＜Ｔｉ／Ｂａ＜４となるように混合し、前駆体とした後、焼成して前記複合酸化物を得ることを特徴とする、
水分解用光触媒の製造方法。 A method for producing the photocatalyst for water splitting according to any one of claims 1 to 4,
A raw material containing titanium atoms and a raw material containing barium atoms are mixed so that the molar ratio of titanium atoms to barium atoms (Ti / Ba) is 3 <Ti / Ba <4 to form a precursor, followed by firing. To obtain the composite oxide .
A method for producing a photocatalyst for water splitting.
請求項５に記載の水分解用光触媒の製造方法。 The composite oxide obtained by the solid phase method or a complex polymerization method,
The manufacturing method of the photocatalyst for water splitting of Claim 5 .
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