JP3837548B2 - Bismuth complex oxide visible light responsive photocatalyst and method for decomposing and removing harmful chemicals using the same - Google Patents
Bismuth complex oxide visible light responsive photocatalyst and method for decomposing and removing harmful chemicals using the same Download PDFInfo
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- 239000000126 substance Substances 0.000 title claims description 31
- 239000011941 photocatalyst Substances 0.000 title claims description 29
- 238000000034 method Methods 0.000 title claims description 12
- 229910052797 bismuth Inorganic materials 0.000 title 1
- JCXGWMGPZLAOME-UHFFFAOYSA-N bismuth atom Chemical compound [Bi] JCXGWMGPZLAOME-UHFFFAOYSA-N 0.000 title 1
- 239000004065 semiconductor Substances 0.000 claims description 10
- 239000002131 composite material Substances 0.000 claims description 9
- 239000000383 hazardous chemical Substances 0.000 claims description 4
- 230000001678 irradiating effect Effects 0.000 claims 1
- IKHGUXGNUITLKF-UHFFFAOYSA-N Acetaldehyde Chemical compound CC=O IKHGUXGNUITLKF-UHFFFAOYSA-N 0.000 description 20
- 238000000354 decomposition reaction Methods 0.000 description 12
- 238000006243 chemical reaction Methods 0.000 description 8
- 239000003054 catalyst Substances 0.000 description 7
- 230000000694 effects Effects 0.000 description 7
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 description 6
- 230000007613 environmental effect Effects 0.000 description 6
- CXKWCBBOMKCUKX-UHFFFAOYSA-M methylene blue Chemical compound [Cl-].C1=CC(N(C)C)=CC2=[S+]C3=CC(N(C)C)=CC=C3N=C21 CXKWCBBOMKCUKX-UHFFFAOYSA-M 0.000 description 5
- 229960000907 methylthioninium chloride Drugs 0.000 description 5
- 238000011160 research Methods 0.000 description 4
- 238000003746 solid phase reaction Methods 0.000 description 4
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 3
- 238000010304 firing Methods 0.000 description 3
- 238000005259 measurement Methods 0.000 description 3
- 229910052751 metal Inorganic materials 0.000 description 3
- 239000002184 metal Substances 0.000 description 3
- 239000000203 mixture Substances 0.000 description 3
- 239000001301 oxygen Substances 0.000 description 3
- 229910052760 oxygen Inorganic materials 0.000 description 3
- 239000002245 particle Substances 0.000 description 3
- 238000006303 photolysis reaction Methods 0.000 description 3
- 239000002994 raw material Substances 0.000 description 3
- 239000004408 titanium dioxide Substances 0.000 description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 3
- RZVAJINKPMORJF-UHFFFAOYSA-N Acetaminophen Chemical compound CC(=O)NC1=CC=C(O)C=C1 RZVAJINKPMORJF-UHFFFAOYSA-N 0.000 description 2
- 229910010413 TiO 2 Inorganic materials 0.000 description 2
- 238000000862 absorption spectrum Methods 0.000 description 2
- 239000007864 aqueous solution Substances 0.000 description 2
- 238000011161 development Methods 0.000 description 2
- 150000002013 dioxins Chemical class 0.000 description 2
- 239000010419 fine particle Substances 0.000 description 2
- 239000011521 glass Substances 0.000 description 2
- 229940088597 hormone Drugs 0.000 description 2
- 239000005556 hormone Substances 0.000 description 2
- 230000001590 oxidative effect Effects 0.000 description 2
- 239000000575 pesticide Substances 0.000 description 2
- 238000000746 purification Methods 0.000 description 2
- 239000005297 pyrex Substances 0.000 description 2
- 238000006722 reduction reaction Methods 0.000 description 2
- 229910015902 Bi 2 O 3 Inorganic materials 0.000 description 1
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 1
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- 239000003905 agrochemical Substances 0.000 description 1
- 150000004703 alkoxides Chemical class 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
- 229910000416 bismuth oxide Inorganic materials 0.000 description 1
- 230000003197 catalytic effect Effects 0.000 description 1
- 238000004140 cleaning Methods 0.000 description 1
- 238000000975 co-precipitation Methods 0.000 description 1
- 239000011248 coating agent Substances 0.000 description 1
- 238000000576 coating method Methods 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 239000000498 cooling water Substances 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- TYIXMATWDRGMPF-UHFFFAOYSA-N dibismuth;oxygen(2-) Chemical compound [O-2].[O-2].[O-2].[Bi+3].[Bi+3] TYIXMATWDRGMPF-UHFFFAOYSA-N 0.000 description 1
- 239000000975 dye Substances 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
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- 238000004817 gas chromatography Methods 0.000 description 1
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- 238000000227 grinding Methods 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 230000004298 light response Effects 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 229910021645 metal ion Inorganic materials 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- 239000004570 mortar (masonry) Substances 0.000 description 1
- 238000013032 photocatalytic reaction Methods 0.000 description 1
- 230000015843 photosynthesis, light reaction Effects 0.000 description 1
- 238000006116 polymerization reaction Methods 0.000 description 1
- 239000002243 precursor Substances 0.000 description 1
- 238000011002 quantification Methods 0.000 description 1
- 230000005855 radiation Effects 0.000 description 1
- 150000003839 salts Chemical class 0.000 description 1
- 208000008842 sick building syndrome Diseases 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
- 238000003756 stirring Methods 0.000 description 1
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- 239000010409 thin film Substances 0.000 description 1
Description
【０００１】
【発明の属する技術分野】
本発明は、酸化ビスマスを含む特定組成の複合酸化物半導体で、太陽光などに含まれる紫外線および可視光線を効率よく吸収する光応答性に優れた光触媒に関する。とりわけ、有害化学物質に対してこれを分解する能力に優れた高活性有害物質分解用光触媒とこの触媒を用いた有害化学物質分解除去方法に関するものである。
【０００２】
【従来の技術と発明が解決しようとする課題】
２０世紀の急激な経済成長がもたらした負の遺産である地球環境問題は、深刻になりつつある。ダイオキシンなどの環境ホルモン物質は勿論の事、水中や大気中の農薬や悪臭物質、さらには、居住空間でのシックハウス症候群など健康被害の原因になっている化学物質なども人類の安全で、快適な生活を脅かしている。これらの有害物質の発生を抑え、また既に発生してしまったものについて素早く取り除く技術開発が求められている。
【０００３】
光触媒では、そのバンドギャップ以上のエネルギーを吸収すると価電子帯からの電子励起によって正孔と電子が生成される。これらは強い酸化、還元力を持つため、周りの化学物質を酸化、あるいは還元することができる。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広く検討され、有効な環境浄化材として期待されている。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る。二酸化チタンはバンドギャップが３．２ｅＶあるため、４００ｎｍより短い紫外光線の照射下でのみ活性を示す。そのため、現在の応用例としては屋外、もしくは紫外線ランプ存在下のみで実用されている。
【０００４】
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、可視光領域の光に対して触媒活性を有する光触媒の開発が望まれている。
【０００５】
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その使用しうる波長領域が広がった分効率が格段に向上すると期待できる。従来の二酸化チタンでは紫外線のない屋内などで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。
【０００６】
【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のみにとどまらず、可視光も効率よく吸収する新規な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、有害物質に光を照射し、当該有害物質を分解するなど有害物質の無害化処理方法を提供しようと云うものである。本発明者を含む研究グループにおいては、これまでにも地球的規模の環境対策への取り組みの一環として光触媒に関して各種提案、発明をしてきた（これについては、下記特許文献１ないし５が挙げられるが、これらは現在、特許出願を申請中であり、まだ公開されていないため、従来技術として文献名を挙げることができず、これに代わり本発明者等において開発した先行技術を出願番号によって記載する。）。
本発明もその研究の一環としてなされたものであり、その特徴は、これまでに提案されてきた上記光触媒とは組成的に全く異なる新規な触媒を開発することに成功したものである。本発明は、この成功に基づいてなされたものである。
【０００７】
【特許文献１】
特許願２００１−２２１１４８号
【特許文献２】
特許願２００２−５９８０４号
【特許文献３】
特許願２００２−２２５２９６号
【特許文献４】
特許願２００3−７３２９４号
【特許文献５】
特許願２００3−７３２９５号
【０００８】
【課題を解決するための手段】
すなわち、本発明者等においては、鋭意研究した結果、上記の課題は、下記（１）〜（３）に記載の手段により解決し、達成することに成功したものである。
【０００９】
（１）一般式（Ｉ）：ＭＢｉ2Ｏ4で表される複合酸化物半導体からなる可視光応答性光 触媒。
式中、ＭはＣａ、Ｓｒ、Ｂａから選ばれる少なくとも１種の元素を表す。
（２）前記（１）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。
（３）前記（２）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除去方法。
【００１０】
【発明の実施の形態】
以下、本発明を具体的に説明するが、これらは何れも本発明の具体的な一つの実施例を開示しているものであって、本発明はこれに限られるものではない。
【００１１】
本発明の請求項第１項に記載する複合酸化物ＭＢｉ2Ｏ4で表される複合酸化物半導体からなる光触媒は、ＭとしてＣａ、Ｓｒ、Ｂａを１種又は２種以上含むものであり、具体的には例えばＣａＢｉ2Ｏ4、ＳｒＢｉ2Ｏ4、又はＢａＢｉ2Ｏ4、さらにはＭサイトに前記複数の元素を含むものも有効であり、これらを含むものである。
【００１２】
本発明の複合酸化物半導体を得るためには、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ができる。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。
【００１３】
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さらに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１μｍ以下である。また微粒子を成型して板状を始め種々の形状に成形し、使用することもできる。他の適宜形状をした担体に担持させて使用することも一つの態様であり、さらには薄膜状にコーティングして使用することもできる。
【００１４】
本発明の光触媒は、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、有害化学物質の分解のように気相反応でも良い。
【００１５】
（実施例）
以下、本発明を具体的に実施例に基づいて詳細に説明する。以下の実施例においては、ＢａＢｉ2Ｏ4の合成を固相反応法によって行った。
【００１６】
実施例１；
ＢａＢｉ2Ｏ4を固相反応法によって合成した。
例えば、１０ｇのＢａＢｉ2Ｏ4を合成する場合はＢａＣＯ3を３．１８６ｇとＢｉ2Ｏ3を７．４５５ｇそれぞれ秤量した。これをアルミナるつぼに入れて、大気圧雰囲気下に設置された電気炉中で７００℃、５時間保持し予備反応させた後、９００℃で１２時間焼結した。焼成終了後、この焼成物を乳鉢で１０mｍ以下の大きさに粉砕した。
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６４０ｎｍ以上の可視光領域まで吸収を示し、バンドキャップは１．９ｅＶ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。
１．５ｇのＢａＢｉ2Ｏ4で８３７ｐｐｍのアセトアルデヒドの分解試験を行った。光源には３００ＷＸｅランプを用い、光による熱効果を防ぐための冷却水セルを通してから反応セルに照射させた。反応セルとしてはパイレックスガラス（コーニング社の登録商標）製のものを用いた。アセトアルデヒドの分解産物のＣＯ2の検出及び定量はガスクロマトグラフィーで行い、ＣＯ2の発生量からアセトアルデヒドの分解率を計算した。その結果を表１に示す。
その結果、４２０ｎｍのフィルターを通した可視光照射下でアセトアルデヒドは、僅か４０分程度で９５％以上が分解された。
【００１７】
実施例２；
ＢａＢｉ2Ｏ4光触媒によるアセトアルデヒド分解の光波長依存性を調べた。実施例１においてＸｅランプの窓に５８０ｎｍより長い光のみを通すカットオフフィルターを挿入し、アセトアルデヒドの光分解反応を行った。
その結果、５８０ｎｍのフィルターを通した可視光照射下でも僅か２０分間で約６０％のアセトアルデヒドの分解が確認された。
【００１８】
実施例３；
０．３ｇのＢａＢｉ2Ｏ4を１５．３ｍｇ／ｌのメチレンブルー水溶液１００ｍｌに懸濁しメチレンブルーの光分解反応を行った。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ガラス（コーニング社の登録商標）製のものを用いた。紫外−可視吸収スペクトル測定により、メチレンブルーの光分解による濃度変化を調べた。その結果、４２０ｎｍのフィルターを通した可視光照射下で６０分間でメチレンブルーメチレンブルーが９０％以上分解できたことが判明した。
【００１９】
比較例１；
代表的な光触媒であるＴｉＯ2を使用してアセトアルデヒド分解の光波長依存性（３６０ｎｍ以上）を調べた。測定に使用した機器は実施例１と同じであった。
その結果、２０分間異なる波長の光を照射したところ、３６０ｎｍの紫外光で約５０％強の活性を示すのが最高で、４００ｎｍ以上の可視光領域へと波長の増加と共に単調に活性を失い、４４０ｎｍ以上では全く活性を示さなかった。測定した波長領域すべてでＢａＢｉ2Ｏ4での活性に及ばず、両者は際だった対比を示した。これより、このＴｉＯ2光触媒は、事実上、可視光照射下においてはアセトアルデヒド分解触媒としては機能しなかった。
【００２０】
以上の結果を表１にまとめて示す。すなわち、表１は、使用された光触媒成分、反応の種類（反応目的）、用いた光源及び波長、光照射時間及び分解率、以上のデータをまとめて示しているものである。
【００２１】
【表１】
【発明の効果】
以上の通り、一般式（Ｉ）；ＭＢｉ2Ｏ4で表される複合酸化物半導体からなる光触媒（式中、ＭはＣａ、Ｓｒ、Ｂａから選ばれる１種又は２種以上の元素を表す）は、光応答できる波長領域が上限６４０ｎｍ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。本発明によれば、可視光エネルギーを利用してアセトアルデヒドの有害化学物質やメチレンブルー等の染料を高効率的に分解できる。また、これらの光触媒を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。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a photocatalyst excellent in photoresponsiveness, which is a composite oxide semiconductor having a specific composition containing bismuth oxide and efficiently absorbs ultraviolet rays and visible rays contained in sunlight. In particular, the present invention relates to a highly active decomposing photocatalyst having an excellent ability to decompose harmful chemical substances and a method for decomposing and removing harmful chemical substances using the catalyst.
[0002]
[Prior art and problems to be solved by the invention]
The global environmental problem, a negative legacy brought about by the rapid economic growth of the 20th century, is becoming more serious. Not only environmental hormone substances such as dioxins, but also pesticides and malodorous substances in the water and in the atmosphere, as well as chemical substances that cause health damage such as sick house syndrome in living spaces are safe and comfortable for humanity. It threatens life. There is a need for technology development that suppresses the generation of these harmful substances and quickly removes those that have already occurred.
[0003]
In the photocatalyst, when energy exceeding the band gap is absorbed, holes and electrons are generated by electron excitation from the valence band. Since these have strong oxidizing and reducing power, they can oxidize or reduce surrounding chemical substances. In recent years, as an applied research of photocatalysts, the use of photocatalysts for the decomposition of harmful chemical substances has been widely studied and is expected as an effective environmental purification material. Application examples such as decomposition of organic substances such as pesticides and malodorous substances in water and air, and self-cleaning of solid surfaces coated with a catalyst have been researched and proposed, but most of them use titanium dioxide. Since titanium dioxide has a band gap of 3.2 eV, it exhibits activity only under irradiation with ultraviolet rays shorter than 400 nm. For this reason, the present application is practically used only outdoors or in the presence of an ultraviolet lamp.
[0004]
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, development of a photocatalyst having catalytic activity for light in the visible light region is desired.
[0005]
Therefore, in the above applied research, if a photocatalyst that can use visible light is developed and can be used, it can be expected that the efficiency will be greatly improved by expanding the usable wavelength region. 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.
[0006]
[Problems to be solved by the invention]
The present invention is intended to provide a novel photocatalyst that absorbs not only ultraviolet rays contained in sunlight and the like but also visible light efficiently, and by using this catalyst, light is irradiated to harmful substances, It is intended to provide a method for detoxifying harmful substances such as decomposing the harmful substances. The research group including the present inventor has so far made various proposals and inventions regarding photocatalysts as part of efforts for global environmental measures (for example, Patent Documents 1 to 5 listed below can be cited). Since these are currently pending patent applications and have not yet been published, the prior art cannot be cited as a prior art, and instead the prior art developed by the inventors is described by the application number. .)
The present invention has also been made as part of its research, and its features have succeeded in developing a novel catalyst that is completely different in composition from the photocatalysts proposed so far. The present invention has been made based on this success.
[0007]
[Patent Document 1]
Patent application 2001-221148 [Patent Document 2]
Patent Application 2002-59804 [Patent Document 3]
Patent application 2002-225296 [Patent Document 4]
Patent Application 2003-73294 [Patent Document 5]
Patent Application No. 2003-73295
[Means for Solving the Problems]
That is, as a result of intensive studies, the inventors have succeeded in solving and achieving the above problems by the means described in (1) to (3) below.
[0009]
(1) A visible light responsive photocatalyst comprising a composite oxide semiconductor represented by the general formula (I): MBi 2 O 4 .
In the formula, M represents at least one element selected from Ca, Sr, and Ba.
(2) A photocatalyst for decomposing harmful chemical substances comprising the complex oxide semiconductor according to (1).
(3) A method for decomposing and removing harmful chemical substances, wherein the harmful chemical substances are irradiated with light containing ultraviolet rays and visible rays in the presence of the photocatalyst for decomposing hazardous chemical substances according to (2).
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail, but these all disclose one specific embodiment of the present invention, and the present invention is not limited to this.
[0011]
The photocatalyst composed of the composite oxide semiconductor represented by the composite oxide MBi 2 O 4 according to claim 1 of the present invention contains one or more of Ca, Sr, and Ba as M, Specifically, for example, CaBi 2 O 4 , SrBi 2 O 4 , or BaBi 2 O 4 , and those containing the plurality of elements at the M site are also effective and include these.
[0012]
In order to obtain the composite oxide semiconductor of the present invention, it is synthesized by a normal solid phase reaction method, that is, by mixing oxides of respective metal components as raw materials at a ratio of a target composition and firing in air under normal pressure. be able to. 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.
[0013]
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 size can be further reduced by grinding with a ball mill or the like. In general, the size of the particles is 10 nm to 200 μm, preferably 1 μm or less. Further, the fine particles can be molded into various shapes including a plate shape and used. It is also one embodiment to use it by supporting it on another appropriately shaped carrier, and it can also be used by coating it in a thin film.
[0014]
The photocatalyst of the present invention can be applied 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. Gas phase reactions such as decomposition of malodorous substances and harmful chemical substances may be used.
[0015]
(Example)
Hereinafter, the present invention will be described in detail based on specific examples. In the following examples, BaBi 2 O 4 was synthesized by a solid phase reaction method.
[0016]
Example 1;
BaBi 2 O 4 was synthesized by a solid phase reaction method.
For example, when synthesizing 10 g of BaBi 2 O 4 , 3.186 g of BaCO 3 and 7.455 g of Bi 2 O 3 were weighed. This was put in an alumina crucible, kept at 700 ° C. for 5 hours in an electric furnace installed under an atmospheric pressure atmosphere, pre-reacted, and then sintered at 900 ° C. for 12 hours. After the completion of firing, the fired product was pulverized to a size of 10 mm or less with a mortar.
The ultraviolet-visible absorption spectrum measurement showed that the present photocatalyst absorbs from the ultraviolet region to the visible light region of 640 nm or more, and the band cap can be estimated to be 1.9 eV or less, and has a visible light response.
A decomposition test of 837 ppm of acetaldehyde was performed with 1.5 g of BaBi 2 O 4 . A 300 WXe lamp was used as a light source, and the reaction cell was irradiated after passing through a cooling water cell for preventing a heat effect due to light. A reaction cell made of Pyrex glass (registered trademark of Corning) was used. Detection and quantification of CO 2 of the decomposition product of acetaldehyde was performed by gas chromatography, and the decomposition rate of acetaldehyde was calculated from the amount of CO 2 generated. The results are shown in Table 1.
As a result, 95% or more of the acetaldehyde was decomposed in only about 40 minutes under visible light irradiation through a 420 nm filter.
[0017]
Example 2;
The light wavelength dependence of acetaldehyde decomposition by BaBi 2 O 4 photocatalyst was investigated. In Example 1, a cut-off filter that allows only light longer than 580 nm to pass was inserted into the window of the Xe lamp, and the photodecomposition reaction of acetaldehyde was performed.
As a result, it was confirmed that about 60% of acetaldehyde was decomposed in only 20 minutes even under visible light irradiation through a 580 nm filter.
[0018]
Example 3;
0.3 g of BaBi 2 O 4 was suspended in 100 ml of a 15.3 mg / l methylene blue aqueous solution to carry out a photolysis reaction of methylene blue. Light was irradiated from the outside while stirring with a magnetic stirrer. A 300 WXe lamp was used as the light source, and a Pyrex glass (registered trademark of Corning) was used as the reaction cell. The concentration change due to the photolysis of methylene blue was examined by ultraviolet-visible absorption spectrum measurement. As a result, it was found that 90% or more of methylene blue could be decomposed in 60 minutes under irradiation with visible light through a 420 nm filter.
[0019]
Comparative Example 1;
Using TiO 2 which is a typical photocatalyst, the light wavelength dependence (360 nm or more) of acetaldehyde decomposition was examined. The equipment used for the measurement was the same as in Example 1.
As a result, when irradiated with light of a different wavelength for 20 minutes, it is best to show an activity of about 50% or more in 360 nm ultraviolet light, and the activity monotonously loses as the wavelength increases to a visible light region of 400 nm or more, No activity was shown at 440 nm or more. The measured wavelength range did not reach the activity with BaBi 2 O 4 , and both showed remarkable contrast. Thus, this TiO 2 photocatalyst did not function effectively as an acetaldehyde decomposition catalyst under visible light irradiation.
[0020]
The above results are summarized in Table 1. That is, Table 1 collectively shows the photocatalyst component used, the type of reaction (reaction purpose), the light source and wavelength used, the light irradiation time and decomposition rate, and the above data.
[0021]
[Table 1]
【The invention's effect】
As described above, a photocatalyst composed of a composite oxide semiconductor represented by the general formula (I); MBi 2 O 4 (wherein M represents one or more elements selected from Ca, Sr and Ba) The wavelength range in which photoresponse is possible extends to visible light with an upper limit of 640 nm, and considering that the conventional photocatalyst functioned only in the ultraviolet light range, the wavelength range that can be used effectively is greatly expanded, and its significance is extremely large. . According to the present invention, it is possible to decompose acetaldehyde harmful chemicals and dyes such as methylene blue with high efficiency using visible light energy. In addition, these photocatalysts may be used in other chemical 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.
Claims (3)
式中、ＭはＣａ、Ｓｒ、Ｂａから選ばれる少なくとも１種の元素を表す。A visible light-responsive photocatalyst comprising a composite oxide semiconductor represented by the general formula (I): MBi 2 O 4 .
In the formula, M represents at least one element selected from Ca, Sr, and Ba.
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