JP3834625B2 - Indium barium composite oxide visible light responsive photocatalyst, method for producing hydrogen using this photocatalyst, and method for decomposing harmful chemical substances - Google Patents
Indium barium composite oxide visible light responsive photocatalyst, method for producing hydrogen using this photocatalyst, and method for decomposing harmful chemical substances Download PDFInfo
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- JP3834625B2 JP3834625B2 JP2002225296A JP2002225296A JP3834625B2 JP 3834625 B2 JP3834625 B2 JP 3834625B2 JP 2002225296 A JP2002225296 A JP 2002225296A JP 2002225296 A JP2002225296 A JP 2002225296A JP 3834625 B2 JP3834625 B2 JP 3834625B2
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- photocatalyst
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Links
- 239000011941 photocatalyst Substances 0.000 title claims description 53
- 239000001257 hydrogen Substances 0.000 title claims description 40
- 229910052739 hydrogen Inorganic materials 0.000 title claims description 40
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 title claims description 37
- 239000000126 substance Substances 0.000 title claims description 25
- 238000000034 method Methods 0.000 title claims description 20
- 239000002131 composite material Substances 0.000 title claims description 12
- 238000004519 manufacturing process Methods 0.000 title claims description 11
- NXRQJDUACMTWJF-UHFFFAOYSA-N [In].[Ba] Chemical compound [In].[Ba] NXRQJDUACMTWJF-UHFFFAOYSA-N 0.000 title 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 28
- 239000004065 semiconductor Substances 0.000 claims description 23
- 150000001875 compounds Chemical class 0.000 claims description 6
- 239000000383 hazardous chemical Substances 0.000 claims description 6
- 230000001678 irradiating effect Effects 0.000 claims description 6
- 150000002431 hydrogen Chemical class 0.000 claims description 4
- 229910052759 nickel Inorganic materials 0.000 claims description 2
- 229910052697 platinum Inorganic materials 0.000 claims description 2
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 21
- 239000003054 catalyst Substances 0.000 description 16
- KRKNYBCHXYNGOX-UHFFFAOYSA-N citric acid Chemical compound OC(=O)CC(O)(C(O)=O)CC(O)=O KRKNYBCHXYNGOX-UHFFFAOYSA-N 0.000 description 12
- 238000006243 chemical reaction Methods 0.000 description 11
- 238000000354 decomposition reaction Methods 0.000 description 11
- 239000000203 mixture Substances 0.000 description 9
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 8
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 8
- 239000001301 oxygen Substances 0.000 description 8
- 229910052760 oxygen Inorganic materials 0.000 description 8
- 230000003197 catalytic effect Effects 0.000 description 7
- 239000007864 aqueous solution Substances 0.000 description 6
- 238000010438 heat treatment Methods 0.000 description 6
- 230000000694 effects Effects 0.000 description 5
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 description 4
- 239000001569 carbon dioxide Substances 0.000 description 4
- 229910002092 carbon dioxide Inorganic materials 0.000 description 4
- 230000000052 comparative effect Effects 0.000 description 4
- 238000006116 polymerization reaction Methods 0.000 description 4
- 238000006722 reduction reaction Methods 0.000 description 4
- RZVAJINKPMORJF-UHFFFAOYSA-N Acetaminophen Chemical compound CC(=O)NC1=CC=C(O)C=C1 RZVAJINKPMORJF-UHFFFAOYSA-N 0.000 description 3
- 229910002651 NO3 Inorganic materials 0.000 description 3
- NHNBFGGVMKEFGY-UHFFFAOYSA-N Nitrate Chemical compound [O-][N+]([O-])=O NHNBFGGVMKEFGY-UHFFFAOYSA-N 0.000 description 3
- 239000000446 fuel Substances 0.000 description 3
- 238000004817 gas chromatography Methods 0.000 description 3
- 239000011521 glass Substances 0.000 description 3
- 238000005470 impregnation Methods 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- 229910052751 metal Inorganic materials 0.000 description 3
- 239000002184 metal Substances 0.000 description 3
- 238000002156 mixing Methods 0.000 description 3
- 239000002245 particle Substances 0.000 description 3
- 238000006303 photolysis reaction Methods 0.000 description 3
- 239000005297 pyrex Substances 0.000 description 3
- 239000002994 raw material Substances 0.000 description 3
- 238000003756 stirring Methods 0.000 description 3
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 2
- 239000003905 agrochemical Substances 0.000 description 2
- QVQLCTNNEUAWMS-UHFFFAOYSA-N barium oxide Chemical compound [Ba]=O QVQLCTNNEUAWMS-UHFFFAOYSA-N 0.000 description 2
- 239000013078 crystal Substances 0.000 description 2
- 230000007613 environmental effect Effects 0.000 description 2
- 239000010419 fine particle Substances 0.000 description 2
- 238000010304 firing Methods 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 2
- 239000011259 mixed solution Substances 0.000 description 2
- 229910017604 nitric acid Inorganic materials 0.000 description 2
- 230000001590 oxidative effect Effects 0.000 description 2
- 239000000843 powder Substances 0.000 description 2
- 150000003839 salts Chemical class 0.000 description 2
- 238000003746 solid phase reaction Methods 0.000 description 2
- 239000000243 solution Substances 0.000 description 2
- 239000004408 titanium dioxide Substances 0.000 description 2
- 238000010792 warming Methods 0.000 description 2
- WKBOTKDWSSQWDR-UHFFFAOYSA-N Bromine atom Chemical class [Br] WKBOTKDWSSQWDR-UHFFFAOYSA-N 0.000 description 1
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 description 1
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- 238000000862 absorption spectrum Methods 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 150000004703 alkoxides Chemical class 0.000 description 1
- 238000004577 artificial photosynthesis Methods 0.000 description 1
- BVKZGUZCCUSVTD-UHFFFAOYSA-N carbonic acid Chemical class OC(O)=O BVKZGUZCCUSVTD-UHFFFAOYSA-N 0.000 description 1
- 150000004649 carbonic acid derivatives Chemical class 0.000 description 1
- 238000004140 cleaning Methods 0.000 description 1
- 238000000975 co-precipitation Methods 0.000 description 1
- 150000002013 dioxins Chemical class 0.000 description 1
- 238000005868 electrolysis reaction Methods 0.000 description 1
- 238000005265 energy consumption Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 239000003344 environmental pollutant Substances 0.000 description 1
- 230000001747 exhibiting effect Effects 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 238000010574 gas phase reaction Methods 0.000 description 1
- 238000000227 grinding Methods 0.000 description 1
- 229940088597 hormone Drugs 0.000 description 1
- 239000005556 hormone Substances 0.000 description 1
- 229910003437 indium oxide Inorganic materials 0.000 description 1
- PJXISJQVUVHSOJ-UHFFFAOYSA-N indium(iii) oxide Chemical compound [O-2].[O-2].[O-2].[In+3].[In+3] PJXISJQVUVHSOJ-UHFFFAOYSA-N 0.000 description 1
- 150000002496 iodine Chemical class 0.000 description 1
- FQXXSQDCDRQNQE-UHFFFAOYSA-N markiertes Thebain Natural products COC1=CC=C2C(N(CC3)C)CC4=CC=C(OC)C5=C4C23C1O5 FQXXSQDCDRQNQE-UHFFFAOYSA-N 0.000 description 1
- 229910021645 metal ion Inorganic materials 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 239000003345 natural gas Substances 0.000 description 1
- GNRSAWUEBMWBQH-UHFFFAOYSA-N nickel(II) oxide Inorganic materials [Ni]=O GNRSAWUEBMWBQH-UHFFFAOYSA-N 0.000 description 1
- 229910000510 noble metal Inorganic materials 0.000 description 1
- QKQQEIVDLRUZRP-UHFFFAOYSA-N northebaine Natural products COC1=CC=C2C(NCC3)CC4=CC=C(OC)C5=C4C23C1O5 QKQQEIVDLRUZRP-UHFFFAOYSA-N 0.000 description 1
- 239000005416 organic matter Substances 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 230000001699 photocatalysis Effects 0.000 description 1
- 238000013032 photocatalytic reaction Methods 0.000 description 1
- 238000002256 photodeposition Methods 0.000 description 1
- 230000001443 photoexcitation Effects 0.000 description 1
- 230000015843 photosynthesis, light reaction Effects 0.000 description 1
- 231100000614 poison Toxicity 0.000 description 1
- 239000002243 precursor Substances 0.000 description 1
- 238000000746 purification Methods 0.000 description 1
- 230000005855 radiation Effects 0.000 description 1
- 238000005215 recombination Methods 0.000 description 1
- 230000006798 recombination Effects 0.000 description 1
- 238000006057 reforming reaction Methods 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 230000004043 responsiveness Effects 0.000 description 1
- 238000003980 solgel method Methods 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 238000001228 spectrum Methods 0.000 description 1
- 239000000758 substrate Substances 0.000 description 1
- 238000001308 synthesis method Methods 0.000 description 1
- 239000010409 thin film Substances 0.000 description 1
- 239000003440 toxic substance Substances 0.000 description 1
- 229910052723 transition metal Inorganic materials 0.000 description 1
- 150000003624 transition metals Chemical class 0.000 description 1
- 238000002371 ultraviolet--visible spectrum Methods 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
Description
【０００１】
【発明の属する技術分野】
本発明は、酸化バリウムと酸化インジウムの複合酸化物半導体からなる光触媒と、この光触媒を用いてなる水素の製造方法及び有害化学物質分解方法に関する。
【０００２】
【従来の技術及び発明が解決しようとする課題】
地球温暖化が世界的な問題となっている。大気中の二酸化炭素がいまのペースで増え続けると２０３０年には、その濃度は産業革命以前の大気中濃度の２倍になる、と予想されている。その温室効果により、極地方の温度は約１４度上昇し、海面が６０ｃｍ上昇すると地球の生態系や気候変動に大きな悪影響を及ぼすとされている。各国の具体的な二酸化
炭素排出量削減の数値が検討され、日本は２００８年から２０１２年の平均排出量を１９９０年レベルより少なくとも６％削減するよう目標が設定された。人類が２１世紀以降においても持続的な発展を続けるためには、二酸化炭素や環境汚染物質を排出しないクリーンエネルギーの開発が必須となっている。また、既に破壊しつつある環境を浄化することが必要不可欠である。
【０００３】
水素は、熱効率がガソリンの３倍と大きい上に燃えて水に帰し、その際有害物質など一切発生しないまさに究極的な燃料と考えられている。実際、水素を燃料とした燃料電池が競って研究され、近いうちに実用化される勢いである。また、水素自動車や水素タービンなどが、有毒物質を発生しないクリーンなシステムとして、開発が企業を含めて緊急に進められている。そして、水素の合成法は、それらすべての元となるため緊急な課題となっている。現在、水素の殆どは石油や天然ガスなどからのリフォーミング反応、或いは水の電気分解から生成されるが、それは同時に温暖化の原因となる二酸化炭素を発生するか、貴重なエネルギー源を使ってしまうことになる。
【０００４】
一方、一年間で地上に届く太陽エネルギーは人類の年間エネルギー消費量の１万倍に相当するほど莫大である。太陽エネルギーの利用法として、太陽電池や太陽熱利用システムが開発されているが、その利用率はまだまだ不十分である上、大規模のものが困難であり、コストが高いなど問題点が多い。
太陽光の有効利用を実現するためには、無尽蔵な太陽光と水から、可視光半導体光触媒を用いて、クリーンな燃料となる水素と酸素を直接製造することができる人工光合成技術が考えられる。
【０００５】
光触媒は、そのバンドギャップ以上のエネルギーを吸収すると、正孔と電子を生成し、これらがそれぞれ水と酸化反応、還元反応を行い、酸素、水素を発生させる。この光触媒の実用化を考えた場合、光源として太陽光の利用は不可欠である。地表に降り注ぐ太陽光は、可視光である波長５００ｎｍ付近に放射の最大強度をもっており、波長４００〜７５０ｎｍの可視光領域のエネルギー量は全太陽光の約４３％である。一方、波長４００ｎｍ以下の紫外線領域では５％にも満たない。従って、太陽光スペクトルを効率よく利用するためには、可視光の光にも触媒活性をもつ光触媒が望まれている。
【０００６】
しかし、従来の多くの半導体光触媒はエネルギーの高い紫外光を照射したときには水素を生成できるが、可視光応答性の半導体光触媒による水素製造の検討例は非常に限られており、かつ活性も低かった。太陽光を利用するためには可視光の有効利用が可能な新規な光触媒の開発が必要不可欠である。
【０００７】
また近年、光触媒の応用研究として、光触媒を有害化学物質の分解に使用することがその分野で広く検討されている。水中や大気中の農薬や悪臭物質などの有機物の分解や触媒を塗布した固体表面のセルフクリーニングなどの応用例が研究、提言されているが、その大部分は二酸化チタンを用いたものであり、しかも可視光線ではほとんど機能しないものであった。
したがって、上記の応用研究おいて、可視光が利用できる光触媒を開発し、使用することができれば効率が向上すると期待できる。また、従来の二酸化チタンでは紫外線のない屋内などの利用が困難であったが、可視光が利用できるようになれば、応用できる市場が大幅に拡大できる。その時重要なのが伝導帯の準位である。酸化物半導体の価電子帯の正孔は酸化能力が非常に強く、水や多くの有機物といった電子供与体を酸化することができる。その時、同時に生成した伝導帯の電子は空気中の酸素を還元することで消費される。つまり、伝導帯準位が酸素の還元準位より負でなくてはならない。水素を発生できる光触媒は酸素を還元できるポテンシャルを持つ新規な均一系の光触媒で、上記の分野への応用が期待できる。
【０００８】
【発明が解決しようとする課題】
本発明は太陽光などに含まれる紫外線を効率よく吸収する光触媒を提供しようとするものであり、この触媒を使用することによって、有害物質や水素含有化合物に光を照射し、該有害物質あるいは水素含有化合物を分解し、以て、有害物質の無害化処理方法或いは水素の生成、製造方法を提供しようと云うものである。
【０００９】
【課題を解決するための手段】
そのため本発明者等においては、鋭意研究した結果、上記の目的は、下記（１）〜（８）手段により解決し、達成しうることに成功した。
【００１０】
その第１の解決手段は、（１）一般式：Ｂａ ４ Ｉｎ ６ Ｏ １３ で表されてなる複合酸化物半導体からなる光触媒からなる光触媒によって、解決を図るものである。
【００１１】
その第２の解決手段は、（２）前記（１）項に記載の光触媒に、Ｐｔ、Ｎｉ、ＮｉＯ Ｘ （ｘは０を超え、１以下の値を表す。）ＩｒＯ ２ 、ＲｕＯ ２ からなる群から選ばれた１種又は２種以上の成分からなる助触媒を配合し、含有させてなる光触媒によって解決するものである。
以下、解決手段を列記すると、次のようになる。
（３） 前記（１）ないし（２）の何れか１項に記載の複合酸化物半導体からなる水素製造用光触媒。
（４） 前記（３）に記載の水素製造用光触媒の存在下、水素含有化合物に紫外線および可視光線を含む光を照射することを特徴とする水素の製造方法。
【００１２】
（５） 前記（１）ないし（２）の何れか１項に記載の複合酸化物半導体からなる水分解用光触媒。
（６） 前記（５）に記載の水分解用光触媒の存在下、水に紫外線および可視光線を含む光を照射することを特徴とする水素の製造方法。
（７） 前記（１）ないし（２）の何れか１項に記載の複合酸化物半導体からなる有害化学物質分解用光触媒。
（８） 前記（７）に記載の有害化学物質分解用光触媒の存在下、有害化学物質に紫外線および可視光線を含む光を照射することを特徴とする有害化学物質分解方法。
【００１３】
【発明の実施の形態】
以下、本発明を実施例によって具体的に説明するが、これらはあくまでも本発明を容易に理解しうるようにするための一助であって、本発明はこれら実施例に限られるものではない。
【００１４】
本願発明の第１の光触媒は、一般式：Ｂａ４Ｉｎ６Ｏ１３で表されてなる複合酸化物半導体からなる光触媒である。
【００１５】
本発明の複合酸化物半導体は、通常の固相反応法、すなわち原料となる各金属成分の酸化物を目的組成の比率で混合し、常圧下空気中で焼成することで合成することもできる。昇華し易い原料では少し多めに加える必要がある。また、金属アルコキシドや金属塩を原料とした各種ゾルゲル法、共沈法、錯体重合法など様々な方法も用いられる。その中には酸化物前駆体を調製し、焼成することで合成することも含むものである。
【００１６】
本発明の光触媒の形状は、光を有効に利用するために微粒子で表面積の大きいことが望ましい。固相反応法で調製した酸化物は粒子が大きく表面積が小さいが、ボールミルなどで粉砕を行うことで粒子径を小さくできる。一般には粒子の大きさは１０ｎｍ〜２００μｍ、好ましくは５０μｍ以下である。また微粒子を成型して板状として使用することもできる。或いは他の材質に薄膜状にコーティングして使用することもできる。
【００１７】
更に、本発明の半導体よりなる光触媒に対して、助触媒であるＰｔなどの貴金属、Ｎｉなどの遷移金属、ＮｉＯＸ（ｘは０を超え、１以下の値を表す。）やＩｒＯ２、ＲｕＯ２等酸化物の担持等光触媒製造に通常用いられるような修飾を行うことができる。担持方法は含浸法や光電着法などで行うことが出来る。含浸法では、光触媒活性種の塩化物、硝酸塩等の化合物の水溶液を用いて半導体に含浸させた後、１００〜２００℃で約２〜５時間乾燥して、８００℃以下、好ましいのは２００〜５００℃でかつ還元性雰囲気及び／又は酸化雰囲気下で２〜５時間焼成する。 助触媒量は０．０１〜１０ｗｔ％、好ましくは０．１〜５ｗｔ％である。
【００１８】
また、水の分解反応を行う際に用いる反応溶液は、純水に限らず、通常、水の分解反応によく用いられるように、炭酸塩や炭酸水素塩、ヨウ素塩、臭素塩等の塩類を混ぜた水を用いてもよい。そして、上記水溶液に本発明の光触媒を添加する。触媒の添加量は、基本的に入射した光が効率よく吸収できる量を選ぶ。照射面積２５ｃｍ２に対して０．０５〜１０ｇ、好ましくは０．２〜３ｇである。このように光分解用触媒を添加した水溶液に光を照射することによって水が分解し、水素が発生する。照射する光の波長は半導体の吸収がある領域の波長の光を含むことが必要である。本発明では太陽光を照射してもよい。
【００１９】
本発明の光触媒は、水の分解だけでなく多くの光触媒反応に応用できる。
たとえば有機物の分解の場合、アルコールや農薬、悪臭物質などは一般に電子供与体として働き、正孔によって酸化分解されるとともに、電子によって水素が発生するか、酸素が還元される。反応形態は、有機物を含む水溶液に触媒を懸濁して光照射しても良いし、触媒を基板に固定しても良い。悪臭物質の分解のように気相反応でも良い。
【００２０】
（実施例）
以下、本発明を実施例に基づいて詳細に説明する。但し、以下の実施例において用いた、Ｂａ４Ｉｎ６Ｏ１３よりなる光触媒は、錯体重合法により調整した。
【００２１】
実施例１：
Ｂａ４Ｉｎ６Ｏ１３を下記要領に基づき錯体重合法により調整した。すなわち、次の手順によってＢａ４Ｉｎ６Ｏ１３を１０ｇ合成した。まず、ＢａＣＯ３を５．４５８ｇとＩｎ（ＮＯ３）３・３Ｈ２Ｏを１４．７２３５ｇ、クエン酸を１３．７３１５ｇそれぞれ秤量し、まずＢａＣＯ３をビーカーに入れ、硝酸で溶かした後、Ｉｎ（ＮＯ３）３・３Ｈ２Ｏを加え、混ぜながら溶かし、最後にクエン酸を加えた。ホットプレートで１００℃で加熱しながら、マグネットスターラーで混合液をかき混ぜた。やがて水が完全に蒸発し、硝酸塩も分解し、溶液が濃くなったら、スターラーを取りだし、加熱はそのまま続けた。充分加熱したところで、加熱を止め、８０℃の恒温槽で１２時間保持した。さらに、電気炉において４５０℃で２時間焼結し、灰色な多孔質非晶質が得られた。最後に１０００℃で２時間焼成し、黄色みを帯びた粉末化合物が得られた。得られた試料をＸＲＤとＳＥＭ−ＥＤＳを用いて触媒の化学組成と結晶構造とを調べた。その結果、得られた生成物は、単斜晶系に属し、格子定数ａ＝１．５１８７、ｂ＝２．４５２７、ｃ＝０．４１８６７ｎｍ、ｂ＝１１４．６６°であることが判明した。紫外−可視吸収スペクトル測定により、本光触媒は紫外線領域から上限４６０ｎｍの可視光領域まで吸収を示し、バンドキャップが２．７ｅＶ以下と見積もることができ、可視光に対して応答性を示すことがわかった。
有機物の分解が光照射で効率良く進行するかを確認するため、水溶液中のメタノールの分解を行った。触媒はＰｔ（０．１ｗｔ％）を担持した上記酸化物半導体を用いた。１ｇの触媒を純水２２０ｍｌとメタノール５０ｍｌの混合液に懸濁し光分解反応をさせた。閉鎖循環系触媒反応装置を用い、マグネチックスターラーで攪拌しながら外部から光を照射した。光源には ３００ＷＸｅランプを用い、反応セルとしてはパイレックス（登録商標）ガラス製のものを用いた。生成した水素の検出及び定量はガスクロマトグラフィーで行った。その結果、水素が５０ｍｍｏｌ／ｈ定常的に発生した。酸素は発生しなかった。これは正孔によりメタノールが酸化分解される一方で、電子が水を還元し水素を発生する反応が光照射下で進行していることを示していることが分かった。後記する参考例としてあげた、ＢａＩｎ２Ｏ４の触媒と比較すると高い触媒活性を有することが確認された。
【００２２】
参考比較例１：
比較のために錯体重合法によりＢａＩｎ２Ｏ４を１０ｇ合成し、その性能を試験した。まず、ＢａＣＯ３を４．５７９ｇ、Ｉｎ（ＮＯ３）３・３Ｈ２Ｏを１６．４６９５ｇ、クエン酸を１３．７３１５ｇそれぞれ秤量した。まずＢａＣＯ３をビーカーに入れ、硝酸で溶かした後、Ｉｎ（ＮＯ３）３・３Ｈ２Ｏを加え、混ぜながら溶かし、最後にクエン酸を加えた。ホットプレートで１００℃で加熱しながら、マグネットスターラーで混合液をかき混ぜた。やがて水が完全に蒸発し、硝酸塩も分解し、溶液が濃くなったら、スターラーを取りだし、加熱はそのまま続けた。充分加熱したところで、加熱を止め、８０℃の恒温槽で１２時間保持した。さらに、電気炉において４５０℃で２時間焼結し、灰色な多孔質非晶質が得られた。最後に１０００℃で２時間焼成し、黄色みを帯びた粉末化合物が得られた。
ＸＲＤとＳＥＭ−ＥＤＳを用いて触媒の化学組成と結晶構造を調べた。この系は単斜晶系に属し、格子定数ａ＝１．４４３２、ｂ＝０．５８３３、ｃ＝２．０７９２ｎｍ、ｂ＝１１０．０２°であることが判明した。紫外−可視吸収スペクトル測定により、本光触媒は紫外線領域から上限４６０ｎｍの可視光領域まで吸収を示し、バンドキャップが２．７ｅＶ以下と見積もることができ、可視光の応答性を有することがわかった。
上記酸化物半導体の１．０ｗｔ％ＮｉＯＸ担持はＮｉ（ＮＯ３）２水溶液の含侵、２００℃で５時間乾燥して、５００℃で水素還元、さらに２００℃で再酸化によって行った。
１ｇのＮｉＯＸ／ＢａＩｎ２Ｏ４を純水２７０ｍｌに懸濁し水の光分解反応をさせた。閉鎖循環系触媒反応装置を用い、マグネチックスターラーで攪拌しながら外部から光を照射した。光源には３００ＷＸｅランプを用い、反応セルとしてはパイレックス（登録商標）ガラス製のものを用いた。生成した水素の検出及び定量はガスクロマトグラフィーで行った。その結果を図１の表に示す。
その結果、水素発生量は、１２μｍｏｌ／ｈの速度で定常的に発生することがわかったが、その単位時間あたりの水素発生量は、実施例１の光触媒の方が、優れていることが確認された。
【００２３】
参考比較例２：
参考比較例１で得られた触媒に光を照射し、水溶液中に混合したメタノールの分解実験を行った。触媒はＰｔ（０．１ｗｔ％）を担持した上記酸化物半導体を用いた。１ｇの触媒を純水２２０ｍｌとメタノール５０ｍｌの混合液に懸濁し光分解反応をさせた。
閉鎖循環系触媒反応装置を用い、マグネチックスターラーで攪拌しながら外部から光を照射した。光源には３００ＷＸｅランプを用い、反応セルとしてはパイレックス（登録商標）ガラス製のものを用いた。
生成した水素の検出及び定量はガスクロマトグラフィーで行った。その結果、水素が２０ｍｍｏｌ／ｈ定常的に発生した。酸素は発生しなかった。これは正孔によりメタノールが酸化分解される一方で、電子が水を還元し水素を発生する反応が光照射下で進行していることを示している。しかしながら、メタノール分解能による単位時間あたりの水素発生量は、実施例１に示した本発明の光触媒の方が優れていることが確認された。
【００２４】
以上の結果を、図１に示す表１にまとめて示す。すなわち、使用された光触媒成分、担持助触媒の成分とその有無、反応の種類（反応目的）、用いた光源、単位時間あたりの水素ガスの発生量、等の関係を、前記表に示しているものである。
これによると、本発明による実施例の光触媒は、極めて高い触媒活性を有し、単位時間あたりの反応速度が大きいということが明らかにされた。
【００２５】
【発明の効果】
以上の通り、本発明の一般式：Ｂａ ４ Ｉｎ ６ Ｏ １３ で表されてなる複合酸化物半導体からなる光触媒は、光応答できる波長領域が上限４６０ｎｍの可視光まで広がり、これまでの光触媒が、紫外光領域でのみ機能していたことを考えると、有効利用できる波長領域を大きく広げ、その意義は極めて大きい。また、光励起で生じたホール及びエレクトロンが速やかに触媒の表面に移動でき、ホールとエレクトロンの再結合の確率が減少し、光に対して高い触媒活性を示す。本発明によれば、可視光エネルギーを利用して水を分解して水素を生成できる。将来的には人工池に光触媒を敷き詰めれば、無尽蔵の太陽光で効率よく水素が大量に製造できる可能性があり、エネルギー問題の克服につながると言える。また、これらの光触媒を水の分解反応でなく他の化学反応に使用しても一向にかまわない。例えばダイオキシンなどの環境ホルモンや有機物の分解反応、また金属イオンの還元反応に応用することができる。環境浄化などにも大きく寄与できる。以上本発明の複合酸化物半導体光触媒は、光の広い領域に対して活性を有すること如上の通りであり、その特性の故、前示使用例以外にも多様な用途に使われることが期待され、今後その果たす役割は、非常に大きいと考えられる。
【００２６】
【図面の簡単な説明】
【図１】 本発明の実施例及び参考比較例における光触媒活性効果を示す図。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a photocatalyst comprising a composite oxide semiconductor of barium oxide and indium oxide, a method for producing hydrogen and a method for decomposing harmful chemical substances using the photocatalyst.
[0002]
[Prior art and problems to be solved by the invention]
Global warming has become a global problem. If carbon dioxide in the atmosphere continues to increase at the current pace, it is expected that in 2030, its concentration will double that of the pre-industrial level. Due to the greenhouse effect, the temperature in the polar region rises by about 14 degrees, and if the sea level rises by 60 cm, it is said that it will have a serious adverse effect on the earth's ecosystem and climate change. Specific carbon dioxide emission reduction figures for each country were examined, and Japan set a target of reducing average emissions from 2008 to 2012 by at least 6% from the 1990 level. In order for mankind to continue to develop after the 21st century, it is essential to develop clean energy that does not emit carbon dioxide or environmental pollutants. It is also essential to purify the environment that is already being destroyed.
[0003]
Hydrogen is considered to be the ultimate fuel that has three times the thermal efficiency of gasoline and burns back to water, producing no harmful substances. In fact, hydrogen-fueled fuel cells are being researched and put to practical use in the near future. In addition, hydrogen automobiles and hydrogen turbines are urgently being developed by companies and other companies as clean systems that do not generate toxic substances. And the synthesis method of hydrogen is an urgent problem because it is the source of all of them. Currently, most of the hydrogen is generated from reforming reactions from oil and natural gas, or from electrolysis of water, which simultaneously generates carbon dioxide, which causes global warming, or uses valuable energy sources. Will end up.
[0004]
On the other hand, the amount of solar energy that reaches the ground in one year is enormous, equivalent to 10,000 times the annual energy consumption of mankind. As solar energy utilization methods, solar cells and solar heat utilization systems have been developed, but their utilization rate is still insufficient, and large-scale ones are difficult and cost is high.
In order to realize the effective use of sunlight, an artificial photosynthesis technology that can directly produce hydrogen and oxygen as clean fuels from inexhaustible sunlight and water using a visible light semiconductor photocatalyst can be considered.
[0005]
When the photocatalyst absorbs energy greater than its band gap, it generates holes and electrons, which respectively undergo oxidation and reduction reactions with water to generate oxygen and hydrogen. Considering the practical application of this photocatalyst, it is essential to use sunlight as a light source. Sunlight falling on the surface of the earth has a maximum intensity of radiation in the vicinity of a wavelength of 500 nm that is visible light, and the amount of energy in the visible light region having a wavelength of 400 to 750 nm is about 43% of the total sunlight. On the other hand, it is less than 5% in the ultraviolet region with a wavelength of 400 nm or less. Therefore, in order to efficiently use the sunlight spectrum, a photocatalyst having catalytic activity for visible light is desired.
[0006]
However, many conventional semiconductor photocatalysts can produce hydrogen when irradiated with high-energy ultraviolet light, but the examples of hydrogen production using visible light-responsive semiconductor photocatalysts are very limited and their activity is low. . In order to use sunlight, it is essential to develop a new photocatalyst that can effectively use visible light.
[0007]
In recent years, as an applied study of photocatalysts, the use of photocatalysts for the decomposition of harmful chemical substances has been widely studied in the field. Application examples such as decomposition of organic substances such as agricultural chemicals and malodorous substances in the water and air and self-cleaning of solid surfaces coated with catalysts have been researched and proposed, most of which are using titanium dioxide, Moreover, it hardly functioned with visible light.
Therefore, in the above applied research, if a photocatalyst that can use visible light is developed and used, it can be expected that the efficiency will be improved. Further, conventional titanium dioxide has been difficult to use indoors without ultraviolet rays, but if visible light can be used, the applicable market can be greatly expanded. What is important at that time is the level of the conduction band. Holes in the valence band of an oxide semiconductor have a very strong oxidizing ability and can oxidize electron donors such as water and many organic substances. At that time, electrons generated in the conduction band are consumed by reducing oxygen in the air. That is, the conduction band level must be more negative than the oxygen reduction level. A photocatalyst capable of generating hydrogen is a novel homogeneous photocatalyst having a potential to reduce oxygen, and can be expected to be applied to the above-mentioned fields.
[0008]
[Problems to be solved by the invention]
The present invention is intended to provide a photocatalyst that efficiently absorbs ultraviolet rays contained in sunlight and the like. By using this catalyst, the harmful substance or hydrogen-containing compound is irradiated with light, and the harmful substance or hydrogen It is intended to provide a method for detoxifying harmful substances or producing and producing hydrogen by decomposing contained compounds.
[0009]
[Means for Solving the Problems]
Therefore, as a result of intensive studies, the inventors have succeeded in solving and achieving the above object by the following means (1) to ( 8 ).
[0010]
The first means for solving the problem is (1) a photocatalyst comprising a photocatalyst made of a complex oxide semiconductor represented by the general formula: Ba 4 In 6 O 13 .
[0011]
Its second aspect consists (2) wherein (1) the photocatalyst according to claim, Pt, Ni, NiO X (x is greater than 0, represents the value of 1 or less.) IrO 2, RuO 2 It solves by the photocatalyst which mix | blends and contains the promoter which consists of 1 type or 2 or more types of components chosen from the group.
Hereinafter, the solving means will be listed as follows.
(3) A photocatalyst for hydrogen production comprising the composite oxide semiconductor according to any one of (1) to (2).
(4) A method for producing hydrogen, comprising irradiating a hydrogen-containing compound with light containing ultraviolet rays and visible light in the presence of the photocatalyst for producing hydrogen according to (3).
[0012]
(5) A photocatalyst for water splitting comprising the composite oxide semiconductor according to any one of (1) to (2).
(6) A method for producing hydrogen, wherein the water is irradiated with light containing ultraviolet rays and visible light in the presence of the photocatalyst for water splitting according to (5).
(7) A photocatalyst for decomposing harmful chemical substances, comprising the composite oxide semiconductor according to any one of (1) to (2).
(8) A method for decomposing a hazardous chemical substance, comprising irradiating the hazardous chemical substance with light containing ultraviolet rays and visible light in the presence of the photocatalyst for decomposing the hazardous chemical substance according to (7).
[0013]
DETAILED DESCRIPTION OF THE INVENTION
EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples. However, these are only for the purpose of facilitating understanding of the present invention, and the present invention is not limited to these examples.
[0014]
The first photocatalyst of the present invention is a photocatalyst composed of a complex oxide semiconductor represented by the general formula: Ba 4 In 6 O 13 .
[0015]
The composite oxide semiconductor of the present invention can also be synthesized by a normal solid phase reaction method, that is, by mixing oxides of respective metal components as raw materials in a ratio of a target composition and firing in air under normal pressure. It is necessary to add a little more in the raw material which is easy to sublimate. Various methods such as various sol-gel methods, coprecipitation methods, and complex polymerization methods using metal alkoxides and metal salts as raw materials are also used. Among them, an oxide precursor is prepared and synthesized by firing.
[0016]
The shape of the photocatalyst of the present invention is preferably fine particles and has a large surface area in order to effectively use light. Although the oxide prepared by the solid phase reaction method has large particles and a small surface area, the particle diameter can be reduced by grinding with a ball mill or the like. In general, the size of the particles is 10 nm to 200 μm, preferably 50 μm or less. Further, fine particles can be molded and used as a plate. Alternatively, other materials can be coated in a thin film.
[0017]
Furthermore, with respect to the photocatalyst comprising the semiconductor of the present invention, a promoter such as a noble metal such as Pt, a transition metal such as Ni, NiO X (x is greater than 0 and represents a value of 1 or less), IrO 2 , RuO. Modifications such as those normally used for photocatalyst production such as supporting of 2nd oxide can be performed. The supporting method can be performed by an impregnation method or a photo-deposition method. In the impregnation method, a semiconductor is impregnated with an aqueous solution of a photocatalytically active species such as chloride and nitrate, and then dried at 100 to 200 ° C. for about 2 to 5 hours to be 800 ° C. or less, preferably 200 to 200 ° C. Firing is performed at 500 ° C. in a reducing atmosphere and / or an oxidizing atmosphere for 2 to 5 hours. The amount of cocatalyst is 0.01 to 10 wt%, preferably 0.1 to 5 wt%.
[0018]
In addition, the reaction solution used for the water decomposition reaction is not limited to pure water. Usually, salts such as carbonates, hydrogen carbonates, iodine salts and bromine salts are used so that they are often used for water decomposition reactions. Mixed water may be used. And the photocatalyst of this invention is added to the said aqueous solution. The amount of catalyst added is basically selected so that incident light can be efficiently absorbed. 0.05~10g the irradiation area 25 cm 2, preferably 0.2 to 3 g. Thus, by irradiating light to the aqueous solution to which the photolysis catalyst is added, water is decomposed and hydrogen is generated. The wavelength of the light to be irradiated needs to include light having a wavelength in a region where the semiconductor is absorbed. In the present invention, sunlight may be irradiated.
[0019]
The photocatalyst of the present invention can be applied not only to water decomposition but also to many photocatalytic reactions.
For example, in the case of decomposition of organic substances, alcohol, agricultural chemicals, malodorous substances and the like generally act as electron donors, and are oxidatively decomposed by holes, and hydrogen is generated by electrons or oxygen is reduced. As a reaction form, the catalyst may be suspended in an aqueous solution containing an organic substance and irradiated with light, or the catalyst may be fixed to a substrate. A gas phase reaction may be used, such as decomposition of malodorous substances.
[0020]
(Example)
Hereinafter, the present invention will be described in detail based on examples. However, the photocatalyst made of Ba 4 In 6 O 13 used in the following examples was prepared by a complex polymerization method.
[0021]
Example 1:
Ba 4 In 6 O 13 was prepared by a complex polymerization method based on the following procedure. That is, 10 g of Ba 4 In 6 O 13 was synthesized by the following procedure. First, 5.458 g of BaCO 3 , 14.7235 g of In (NO 3 ) 3 .3H 2 O and 13.7315 g of citric acid were weighed. BaCO 3 was first placed in a beaker, dissolved in nitric acid, and then In ( NO 3) 3 · 3H 2 O was added, dissolved while mixing were added finally citric acid. The mixture was stirred with a magnetic stirrer while heating on a hot plate at 100 ° C. When the water was completely evaporated and nitrate was decomposed over time, the stirrer was taken out and the heating was continued. When fully heated, the heating was stopped and the mixture was held in a thermostatic bath at 80 ° C. for 12 hours. Furthermore, it was sintered at 450 ° C. for 2 hours in an electric furnace to obtain a gray porous amorphous material. Finally, it was calcined at 1000 ° C. for 2 hours to obtain a yellowish powder compound. The obtained sample was examined for the chemical composition and crystal structure of the catalyst using XRD and SEM-EDS. As a result, it was found that the obtained product belonged to the monoclinic system and had lattice constants a = 1.5187, b = 2.4527, c = 0.48867 nm, and b = 114.66 °. The UV-Vis absorption spectrum measurement shows that the present photocatalyst absorbs from the ultraviolet region to the visible light region with an upper limit of 460 nm, the band cap can be estimated to be 2.7 eV or less, and is responsive to visible light. It was.
In order to confirm whether decomposition of organic matter proceeded efficiently by light irradiation, methanol in an aqueous solution was decomposed. As the catalyst, the above oxide semiconductor carrying Pt (0.1 wt%) was used. 1 g of the catalyst was suspended in a mixed solution of 220 ml of pure water and 50 ml of methanol and subjected to a photolysis reaction. Using a closed circulation system catalytic reactor, light was irradiated from the outside while stirring with a magnetic stirrer. A 300WXe lamp was used as the light source, and a Pyrex (registered trademark) glass was used as the reaction cell. The generated hydrogen was detected and quantified by gas chromatography. As a result, hydrogen was constantly generated at 50 mmol / h. Oxygen was not generated. This indicates that while the methanol is oxidatively decomposed by holes, the reaction in which electrons reduce water and generate hydrogen proceeds under light irradiation. Compared with the BaIn 2 O 4 catalyst mentioned as a reference example described later, it was confirmed that the catalyst had high catalytic activity.
[0022]
Reference Comparative Example 1:
For comparison, 10 g of BaIn 2 O 4 was synthesized by a complex polymerization method, and its performance was tested. First, 4.579 g of BaCO 3 , 16.4695 g of In (NO 3 ) 3 .3H 2 O, and 13.7315 g of citric acid were weighed. First, BaCO 3 was put in a beaker and dissolved in nitric acid, then In (NO 3 ) 3 .3H 2 O was added, dissolved while mixing, and finally citric acid was added. The mixture was stirred with a magnetic stirrer while heating on a hot plate at 100 ° C. When the water was completely evaporated and nitrate was decomposed over time, the stirrer was taken out and the heating was continued. When fully heated, the heating was stopped and the mixture was held in a thermostatic bath at 80 ° C. for 12 hours. Furthermore, it was sintered at 450 ° C. for 2 hours in an electric furnace to obtain a gray porous amorphous material. Finally, it was calcined at 1000 ° C. for 2 hours to obtain a yellowish powder compound.
The chemical composition and crystal structure of the catalyst were investigated using XRD and SEM-EDS. This system belongs to the monoclinic system, and it was found that the lattice constants a = 1.4432, b = 0.5833, c = 2.0792 nm, and b = 1100.02 °. The UV-visible absorption spectrum measurement showed that the present photocatalyst showed absorption from the ultraviolet region to the visible light region with an upper limit of 460 nm, the band cap could be estimated to be 2.7 eV or less, and had visible light responsiveness.
The oxide semiconductor was supported by 1.0 wt% NiO X by impregnation with an aqueous Ni (NO 3 ) 2 solution, dried at 200 ° C. for 5 hours, reduced by hydrogen at 500 ° C., and reoxidized at 200 ° C.
1 g of NiO X / BaIn 2 O 4 was suspended in 270 ml of pure water, and water was photolyzed. Using a closed circulation system catalytic reactor, light was irradiated from the outside while stirring with a magnetic stirrer. A 300 WXe lamp was used as a light source, and a reaction cell made of Pyrex (registered trademark) glass was used. The generated hydrogen was detected and quantified by gas chromatography. The results are shown in the table of FIG.
As a result, it was found that the hydrogen generation amount was constantly generated at a rate of 12 μmol / h, but it was confirmed that the photocatalyst of Example 1 was superior in the hydrogen generation amount per unit time. It was done.
[0023]
Reference Comparative Example 2:
The catalyst obtained in Reference Comparative Example 1 was irradiated with light, and a decomposition experiment of methanol mixed in an aqueous solution was performed. As the catalyst, the above oxide semiconductor carrying Pt (0.1 wt%) was used. 1 g of the catalyst was suspended in a mixed solution of 220 ml of pure water and 50 ml of methanol and subjected to a photolysis reaction.
Using a closed circulation system catalytic reactor, light was irradiated from the outside while stirring with a magnetic stirrer. A 300 WXe lamp was used as a light source, and a reaction cell made of Pyrex (registered trademark) glass was used.
The generated hydrogen was detected and quantified by gas chromatography. As a result, hydrogen was constantly generated at 20 mmol / h. Oxygen was not generated. This indicates that while the methanol is oxidatively decomposed by holes, the reaction in which electrons reduce water and generate hydrogen proceeds under light irradiation. However, it was confirmed that the amount of hydrogen generated per unit time based on methanol resolution was superior to the photocatalyst of the present invention shown in Example 1.
[0024]
The above results are summarized in Table 1 shown in FIG. That is, the table shows the relationship between the photocatalyst component used, the supported cocatalyst component and its presence, the type of reaction (reaction purpose), the light source used, the amount of hydrogen gas generated per unit time, and the like. Is.
According to this, it was clarified that the photocatalysts of the examples according to the present invention have extremely high catalytic activity and a high reaction rate per unit time.
[0025]
【The invention's effect】
As described above, the photocatalyst composed of the composite oxide semiconductor represented by the general formula: Ba 4 In 6 O 13 of the present invention has a wavelength range in which photoresponse can be extended to visible light having an upper limit of 460 nm. Considering that it functioned only in the ultraviolet region, the wavelength range that can be used effectively is greatly expanded, and its significance is extremely great. In addition, holes and electrons generated by photoexcitation can quickly move to the surface of the catalyst, reducing the probability of recombination of holes and electrons, and exhibiting high catalytic activity for light. According to the present invention, hydrogen can be generated by decomposing water using visible light energy. In the future, if a photocatalyst is laid in an artificial pond, there is a possibility that hydrogen can be efficiently produced in large quantities with inexhaustible sunlight, which can overcome the energy problem. In addition, these photocatalysts may be used for other chemical reactions instead of water decomposition reactions. For example, it can be applied to environmental hormones such as dioxins, organic substance decomposition reactions, and metal ion reduction reactions. It can greatly contribute to environmental purification. As described above, the composite oxide semiconductor photocatalyst of the present invention is active for a wide region of light, and because of its characteristics, it is expected to be used in various applications other than the above-described use examples. The role to play in the future is considered to be very large.
[0026]
[Brief description of the drawings]
FIG. 1 is a graph showing the photocatalytic activity effect in Examples and Reference Comparative Examples of the present invention.
Claims (8)
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| JP5214404B2 (en) * | 2008-10-27 | 2013-06-19 | 三井造船株式会社 | Method for detoxifying persistent organic compounds |
| KR101968643B1 (en) * | 2011-06-15 | 2019-04-12 | 삼성전자주식회사 | Visible light sensitive photocatalyst, method of producing the same, electrochemical water splitting cell, water splitting system, organic material decomposition system comprising the same |
| WO2012173400A2 (en) * | 2011-06-15 | 2012-12-20 | Samsung Electronics Co., Ltd. | Visible light sensitive photocatalyst, method of producing the same, and electrochemical water decomposition cell, water decomposition system, and organic material decomposition system each including the same |
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