JPH1087303A - Method for converting light energy - Google Patents
Method for converting light energyInfo
- Publication number
- JPH1087303A JPH1087303A JP8241506A JP24150696A JPH1087303A JP H1087303 A JPH1087303 A JP H1087303A JP 8241506 A JP8241506 A JP 8241506A JP 24150696 A JP24150696 A JP 24150696A JP H1087303 A JPH1087303 A JP H1087303A
- Authority
- JP
- Japan
- Prior art keywords
- reaction
- light
- aqueous solution
- ions
- oxygen
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
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
-
- 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
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P20/00—Technologies relating to chemical industry
- Y02P20/10—Process efficiency
- Y02P20/133—Renewable energy sources, e.g. sunlight
Abstract
Description
【０００１】[0001]
【発明の属する技術分野】本発明は、光エネルギーを酸
素及び／又は水素に変換させる方法に関するものであ
る。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for converting light energy into oxygen and / or hydrogen.
【０００２】[0002]
【従来の技術】太陽エネルギーの有効利用のために、こ
れを利用し易いエネルギー形態に変換・貯蔵する技術の
研究が盛んに行われている。太陽電池はその代表的な例
であるが、コストが高いために普及が進まず、より安価
なシステムの開発が望まれている。光触媒により水を水
素と酸素に分解するシステムは非常に単純であり、生産
にかかるコストやエネルギーは非常に少なくてすむため
研究が昔から行われているが、現状は変換効率が非常に
低くかつ可視光線が利用できないなどの問題点がある。
光触媒で可視光を利用するには、(1)可視光応答性の半
導体を用いる、（２）色素などの増感剤を用いる、の２
つが考えられる。（１）については、いくつかの可視光
応答性半導体が知られているが、その中で反応中に安定
であり、かつ伝導帯と価電子帯の電位が水の酸化還元電
位に対して適しているものはほとんど知られていない。
そのため半導体光触媒による水の分解は紫外光応答の半
導体でしか成功していない。一方、(2)については、光
合成を模倣していろいろな金属錯体や有機色素に関して
研究されているが、酸素発生反応は４電子反応であるた
め通常の色素では多電子反応は非常にむずかしく、成功
例はない。最近、村松らは酸化チタン半導体光触媒を用
いて次式の反応を行った（日本化学会第７０回春期年会
予稿集,1F736(1996)）。 2Fe(III) ＋ H2O → 2Fe(II) ＋ 1/2O2 ＋ 2H+ （１） この光触媒システムは、水を酸化して酸素を発生すると
いう光合成の素反応の中で最も難しい多電子反応を高効
率で行える点で非常に有用であるが、酸化チタンは可視
光応答性がない半導体であるため、太陽光を利用するこ
とができない。2. Description of the Related Art In order to effectively utilize solar energy, researches on technologies for converting and storing solar energy into an easily usable energy form have been actively conducted. Solar cells are a typical example, but they are not widely used due to high cost, and there is a demand for the development of cheaper systems. Research has been conducted for a long time since the system for decomposing water into hydrogen and oxygen by a photocatalyst is very simple, and the cost and energy required for production are very small. There are problems such as the inability to use visible light.
To use visible light with a photocatalyst, (1) use a semiconductor that responds to visible light, and (2) use a sensitizer such as a dye.
One can be considered. Regarding (1), several visible light responsive semiconductors are known, in which the semiconductor is stable during the reaction, and the potentials of the conduction band and the valence band are suitable for the oxidation-reduction potential of water. Little is known.
For this reason, decomposition of water by a semiconductor photocatalyst has been successful only with a semiconductor that responds to ultraviolet light. On the other hand, for (2), various metal complexes and organic dyes have been studied to imitate photosynthesis. There is no example. Recently, Muramatsu et al. Performed the following reaction using a titanium oxide semiconductor photocatalyst (Proceedings of the 70th Annual Meeting of the Chemical Society of Japan, 1F736 (1996)). 2Fe (III) + H 2 O → 2Fe (II) + 1 / 2O 2 + 2H + (1) The photocatalytic system, the most difficult multi-electron in photosynthesis elementary reaction that oxidizes water to generate oxygen Although very useful in that the reaction can be performed with high efficiency, since titanium oxide is a semiconductor having no responsiveness to visible light, sunlight cannot be used.
【０００３】[0003]
【発明が解決しようとする課題】本発明は、太陽光等の
光エネルギーを化学エネルギーに変換する方法を提供す
ることをその課題とする。SUMMARY OF THE INVENTION An object of the present invention is to provide a method for converting light energy such as sunlight into chemical energy.
【０００４】[0004]
【課題を解決するための手段】本発明者らは、前記課題
を解決すべく鋭意研究を重ねた結果、本発明を完成する
に至った。即ち、鉄(III)イオンを含む水溶液に可視光
応答性の半導体光触媒を接触させるとともに、該半導体
光触媒に可視光を照射して、該水溶液から酸素を発生さ
せることを特徴とする光エネルギーの変換方法が提供さ
れる。また、本発明によれば、鉄(II)イオンを含む水溶
液に紫外光を照射して水素を発生させることを特徴とす
る光エネルギーの変換方法が提供される。さらに、本発
明によれば、鉄(III)イオンを含む水溶液に可視光応答
性の半導体光触媒を接触させるとともに、該半導体光触
媒に可視光を照射して、該水溶液から酸素を発生させる
光エネルギーの変換工程と、鉄(II)イオンを含む水溶液
に紫外光を照射して水素を発生させる光エネルギーの変
換工程からなることを特徴とする光エネルギーの変換方
法が提供される。Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have completed the present invention. That is, while contacting a visible light responsive semiconductor photocatalyst with an aqueous solution containing iron (III) ions, and irradiating the semiconductor photocatalyst with visible light to generate oxygen from the aqueous solution, conversion of light energy. A method is provided. Further, according to the present invention, there is provided a method for converting light energy, which comprises irradiating an aqueous solution containing iron (II) ions with ultraviolet light to generate hydrogen. Further, according to the present invention, a visible light responsive semiconductor photocatalyst is brought into contact with an aqueous solution containing iron (III) ions, and the semiconductor photocatalyst is irradiated with visible light to generate light energy for generating oxygen from the aqueous solution. There is provided a method for converting light energy, which comprises a conversion step and a light energy conversion step of irradiating an aqueous solution containing iron (II) ions with ultraviolet light to generate hydrogen.
【０００５】[0005]
【発明の実施の形態】本発明の光エネルギー変換方法
は、前記（１）式の反応を可視光を用いて進行させる。
（１）式の反応は大きなエネルギー蓄積反応であるため
外部からエネルギーを供給しなければいけない。本発明
では、太陽エネルギーの可視光を用いてこの反応を行わ
せるために、本発明では可視光応答性の半導体光触媒を
用いる。酸素発生は多電子光反応であるが、半導体光触
媒は電子や正孔を多数プールできるので酸素発生能力が
充分備わっている。触媒用の半導体の条件としては、
(i)バンドギャップが可視光吸収できる大きさ、(ii)伝
導帯のポテンシャルがFe(III)/Fe(II)のレッドクス準位
より高い（負に大きい）、(iii)価電子帯のポテンシャ
ルがO2/H2Oのレッドクス順位より低い（正に大きい）、
(iv)反応条件下で安定である、という条件を満たすもの
でなければいけない。可視光応答性の半導体光触媒とし
ては、具体的にはWO3やIn2O3などの単純酸化物、FeTiOx
のような複合酸化物を用いることができる。また、酸化
物以外ではSiCなどが伝導帯ポテンシャルの高い半導体
があり、本発明に適用することができる。BEST MODE FOR CARRYING OUT THE INVENTION In the light energy conversion method of the present invention, the reaction of the above formula (1) is advanced using visible light.
Since the reaction of equation (1) is a large energy storage reaction, energy must be supplied from the outside. In the present invention, a visible light responsive semiconductor photocatalyst is used in the present invention in order to cause this reaction using visible light of solar energy. Oxygen generation is a multi-electron photoreaction, but a semiconductor photocatalyst has a sufficient oxygen generating ability because it can pool many electrons and holes. The conditions of the semiconductor for the catalyst include:
(i) the band gap can absorb visible light, (ii) the conduction band potential is higher (negatively large) than the Redox level of Fe (III) / Fe (II), and (iii) the valence band potential. Is lower than the Redox rank of O 2 / H 2 O (just higher),
(iv) It must satisfy the condition that it is stable under the reaction conditions. Examples of visible light responsive semiconductor photocatalysts include simple oxides such as WO 3 and In 2 O 3 and FeTiOx
Such a composite oxide can be used. In addition, other than oxides, there is a semiconductor having a high conduction band potential, such as SiC, which can be applied to the present invention.
【０００６】半導体は、市販品をそのまま用いても良い
し金属前駆体より合成しても良い。純度はできるだけ高
いことが望ましい。前駆体より水酸化物の沈澱をつくっ
て焼成したり、アンモニウム塩の熱分解、ゾルゲル法な
ど様々な調製法が利用できるが、調製した半導体はでき
るだけ結晶性が良く、かつある程度広い表面積をもつも
のがよい。結晶径の範囲は１〜５０００ｎｍ、好ましく
は２〜２００ｎｍ程度が良い。しかし半導体によっては
調製法が限定されるため、結晶径の制御が難しいものが
あり、その場合には大きな結晶径でも良い。As the semiconductor, a commercially available product may be used as it is or may be synthesized from a metal precursor. It is desirable that the purity be as high as possible. A variety of preparation methods can be used, such as preparing a precipitate of hydroxide from the precursor and baking it, pyrolyzing ammonium salts, and sol-gel method.The prepared semiconductor has good crystallinity as much as possible and has a certain surface area. Is good. The range of the crystal diameter is 1 to 5000 nm, preferably about 2 to 200 nm. However, since the preparation method is limited depending on the semiconductor, it is difficult to control the crystal diameter, and in this case, a large crystal diameter may be used.
【０００７】Fe(III)イオンを含む水溶液は、Fe(III)を
含む水溶性鉄塩、例えば、硫酸鉄(III)を水中に溶解さ
せることによって行うことができる。水溶液中のFe(II
I)イオンの濃度は、水溶液１リットル中、０．０１〜１
００ミリモル、好ましくは０．１〜５０ミリモルであ
る。この水溶液のpHは０〜１２、好ましくは０〜４であ
る。半導体光触媒（以下、単に触媒とも云う）は、水溶
液に接触させる。このための方法としては、触媒微粉末
を水溶液中に懸濁させる方法や、触媒微粉末からなる膜
体を反応器壁上に形成する方法、基板上に触媒微粉末か
らなる膜体を形成し、これを水溶液中に充填する方法等
が挙げられる。前記（１）式の反応は、約８８kJ/mol o
f H2O(pH=O、Fe(III)=1N)のエネルギー蓄積反応（△Ｇ
＜０、アップヒル反応）である。つまり、光エネルギー
を可視光応答光触媒使って化学エネルギーに変換する反
応であり、必要なときに（１）式の逆反応を行いエネル
ギーを取り出すことができる。The aqueous solution containing Fe (III) ions can be prepared by dissolving a water-soluble iron salt containing Fe (III), for example, iron (III) sulfate in water. Fe (II) in aqueous solution
I) The concentration of ions is 0.01 to 1 in 1 liter of aqueous solution.
00 mmol, preferably 0.1 to 50 mmol. The pH of this aqueous solution is 0 to 12, preferably 0 to 4. A semiconductor photocatalyst (hereinafter, also simply referred to as a catalyst) is brought into contact with an aqueous solution. As a method for this, a method of suspending a catalyst fine powder in an aqueous solution, a method of forming a film of catalyst fine powder on a reactor wall, and a method of forming a film of catalyst fine powder on a substrate And a method of filling this into an aqueous solution. The reaction of the formula (1) is performed at about 88 kJ / mol o
Energy storage reaction of fH 2 O (pH = O, Fe (III) = 1N) (△ G
<0, uphill reaction). In other words, this is a reaction that converts light energy into chemical energy using a visible light responsive photocatalyst, and the energy can be extracted by performing the reverse reaction of equation (1) when necessary.
【０００８】本発明の他の光エネルギー変換方法は、下
記（２）式の反応を紫外光を用いて進行させる。 2Fe(II) ＋ 2H+ → 2Fe(III) ＋ H2 （２） 本発明者らの研究によれば、この反応は、Fe(II)自身の
３００ｎｍ以下の紫外光吸収による光反応で効率よく進
行すること及び紫外光応答性半導体光触媒の存在下にお
いて促進されることが見出された。この場合の半導体光
触媒は、(i)反応系に安定に存在し、かつ(ii)伝導帯の
ポテンシャルがH+/H2のレドックス準位より高い（負に
大きい）ことが必要である。このような半導体光触媒と
しては、TiO2やSrTiO3などが利用できる。また、水素発
生の過電圧を減少させるために、白金やニッケル、酸化
ルテニウム等その半導体表面に担持しても良い。In another light energy conversion method of the present invention, the reaction represented by the following formula (2) is advanced using ultraviolet light. 2Fe (II) + 2H + → 2Fe (III) + H 2 (2) According to the research of the present inventors, the reaction is effectively a light reaction by ultraviolet light absorption below 300nm of Fe (II) itself It has been found that it proceeds and is accelerated in the presence of an ultraviolet light responsive semiconductor photocatalyst. In this case, the semiconductor photocatalyst needs to be (i) stably existing in the reaction system, and (ii) having a conduction band potential higher (negatively larger) than the redox level of H + / H 2 . As such a semiconductor photocatalyst, TiO 2 or SrTiO 3 can be used. Further, in order to reduce the overvoltage of hydrogen generation, platinum, nickel, ruthenium oxide or the like may be supported on the semiconductor surface.
【０００９】前記（２）式の反応によれば、光エネルギ
ーを水素に変換させることができ、これにより149kj/mo
lの光エネルギーを蓄積することができる。この場合に
も、前記（１）式の反応の場合と同様に、必要なとき
に、（２）式の逆反応を行い、エネルギーを任意に取り
出すことができる。Fe(II)イオンを含む水溶液は、F(I
I)を含む水溶性鉄塩、例えば硫酸鉄(II)を水中に溶解さ
せることによって得ることができる。水溶液中のFe(II)
イオンの濃度は、水溶液１リットル中、０．０１〜１０
０ミリモル、好ましくは０．１〜５０ミリモルである。
この水溶液のpHは、０〜１２、好ましくは０〜４であ
る。According to the reaction of the above formula (2), light energy can be converted into hydrogen, and as a result, 149 kj / mo
l can store light energy. Also in this case, the energy can be arbitrarily extracted by performing the reverse reaction of the formula (2) when necessary, as in the case of the reaction of the formula (1). The aqueous solution containing Fe (II) ions is F (I
It can be obtained by dissolving a water-soluble iron salt containing I), for example, iron (II) sulfate in water. Fe (II) in aqueous solution
The concentration of ions is 0.01 to 10 per liter of aqueous solution.
0 mmol, preferably 0.1-50 mmol.
The pH of this aqueous solution is from 0 to 12, preferably from 0 to 4.
【００１０】本発明によれば、前記（１）式の反応によ
る光エネルギー変換方法と、前記（２）式の反応による
光エネルギー変換方法を組合わせることにより、結果的
に、下記（３）式のように、水を分解し、光エネルギー
を酸素と水素に変換して蓄積することができる。 Ｈ2Ｏ→１／２ Ｏ2＋Ｈ2 （３） 前記（１）式の反応と（２）式の反応を組合せる方法に
は、前記（１）式と（２）式の反応を同時に進行させる
方法と、前記（１）式の反応と（２）式の反応を別々に
進行させる方法が包含される。前者の方法を実施するに
は、Fe(II)イオンとFe(III)イオンとがある割合で存在
する水溶液中に、（１）式の反応を進行させる光触媒を
存在させ、必要に応じ、（２）式の反応を促進させる光
触媒を存在させ、可視光と紫外光の照射を行う。これに
より、反応初期には（１）式の反応と（２）式の反応の
うち、進行しやすい方の反応が優先して起るが、Fe(II
I)/Fe(II)濃度が平衡になった後では水素と酸素が２／
１のモル比で発生し、（３）式の水の分解反応が起る。
一方、後者の方法を実施するには、最初に（１）式の反
応を進行させる光触媒を存在させて、可視光を照射し
て、（１）式の反応を進行させて酸素を発生させる。こ
れにより、水溶液中のF(II)濃度が高められる。次に、
（２）式の反応を促進させる光触媒の存在下又は非存在
下に、紫外光を照射して、（２）式の反応を進行させて
水素を発生させる。これにより、水溶液中のFe(III)濃
度が増加する。次いで、この水溶液に（１）式の反応を
進行させる光触媒の存在下で可視光を照射することによ
り、酸素を発生させる。このようにして、（１）式の反
応と（２）式の反応を順次繰返し行うことにより、水を
分解し、酸素と水素を別々に発生させることができる。According to the present invention, by combining the light energy conversion method by the reaction of the above formula (1) and the light energy conversion method by the reaction of the above formula (2), as a result, the following formula (3) is obtained. As described above, water can be decomposed and light energy can be converted into oxygen and hydrogen and stored. H 2 O → １ ／ O 2 + H 2 (3) In the method of combining the reaction of the above formula (1) and the reaction of the formula (2), the reactions of the above formulas (1) and (2) proceed simultaneously. And a method in which the reaction of the formula (1) and the reaction of the formula (2) are allowed to proceed separately. In order to carry out the former method, a photocatalyst which promotes the reaction of the formula (1) is present in an aqueous solution in which Fe (II) ions and Fe (III) ions are present in a certain ratio, and if necessary, ( 2) Irradiation of visible light and ultraviolet light is performed in the presence of a photocatalyst that promotes the reaction of the formula. As a result, in the early stage of the reaction, the reaction which proceeds more easily, of the reaction of the formula (1) and the reaction of the formula (2), occurs preferentially.
After the equilibrium I / Fe (II) concentration, hydrogen and oxygen
It occurs at a molar ratio of 1 and the decomposition reaction of water of the formula (3) occurs.
On the other hand, in order to carry out the latter method, first, a photocatalyst which causes the reaction of the formula (1) to proceed is present, and visible light is irradiated to cause the reaction of the formula (1) to proceed to generate oxygen. Thereby, the F (II) concentration in the aqueous solution is increased. next,
Ultraviolet light is irradiated in the presence or absence of a photocatalyst that promotes the reaction of the formula (2) to cause the reaction of the formula (2) to proceed to generate hydrogen. Thereby, the concentration of Fe (III) in the aqueous solution increases. Then, oxygen is generated by irradiating this aqueous solution with visible light in the presence of a photocatalyst that causes the reaction of formula (1) to proceed. In this way, by sequentially repeating the reaction of the formula (1) and the reaction of the formula (2), water can be decomposed and oxygen and hydrogen can be separately generated.
【００１１】Fe(III)/Fe(II)のレッドクスポテンシャル
は全鉄イオン濃度やFe(III)/Fe(II)の割合、pH、陰イオ
ンなどの影響をうける。当然（１）式の反応はFe(III)
イオン濃度が高く、pHも高いほど進行し易い。一方、
（２）式の反応はFe(II)イオン濃度が高く、pHは低い方
がよい。どちらの反応も逆反応と平衡状態にあるため、
反応速度を高め、広い範囲で平衡を移行させるためには
活性の高い触媒及び効率の良い光照射法が重要になる。
また陰イオンの影響も大きい。鉄イオンに対して錯イオ
ン形成性イオン、例えば、CN-イオンが存在すると鉄イ
オンは［Fe(CN)6］3-や［Fe(CN)6］4-という錯イオンを
形成し、レドックスポテンシャルは高くなる（負に大き
くなる）ので酸素発生には不利になるが水素発生には有
利になる。Fe(III)/Fe(II)イオンはアルカリ性では水酸
化物の沈澱を生じてしまうので酸性領域でしか使えない
が、CN-と錯イオンを作ると高いｐＨでも安定であると
いう利点がある。鉄イオンを含む錯イオンを形成させる
には、キレート化剤が用いられるが、このキレート化剤
としては、水に溶けてCNイオンを生成する水溶性シアン
化物(NaCN,KCN,NH4CN,Ca(CN)2,Mg(CN)2等)の他、クエン
酸や、エチレンジアミンテトラ酢酸もしくはその水溶液
塩等が挙げられる。これらのキレート化剤は、鉄イオン
１当量当り、少なくとも１当量、好ましくは１〜６当量
の割合で用いられる。The Redox potential of Fe (III) / Fe (II) is affected by the total iron ion concentration, the ratio of Fe (III) / Fe (II), pH, anions and the like. Naturally, the reaction of equation (1) is Fe (III)
The higher the ion concentration and the higher the pH, the easier the process proceeds. on the other hand,
In the reaction of the formula (2), the Fe (II) ion concentration is preferably high and the pH is preferably low. Because both reactions are in equilibrium with the reverse reaction,
In order to increase the reaction rate and shift the equilibrium over a wide range, a highly active catalyst and an efficient light irradiation method are important.
The effect of anions is also large. When a complex ion forming ion, for example, CN - ion is present with respect to the iron ion, the iron ion forms a complex ion such as [Fe (CN) 6 ] 3− or [Fe (CN) 6 ] 4− , and the redox potential Is high (negatively large), which is disadvantageous for oxygen generation, but advantageous for hydrogen generation. Fe (III) / Fe (II ) ions is not used only in an acidic region because the alkaline occurs precipitation of hydroxides, CN - making complex ions when there is an advantage that it is stable at high pH. To form a complex ion containing iron ions, a chelating agent is used, and as the chelating agent, a water-soluble cyanide (NaCN, KCN, NH 4 CN, Ca (CN) 2 , Mg (CN) 2, etc.), as well as citric acid, ethylenediaminetetraacetic acid, or an aqueous salt thereof. These chelating agents are used in a ratio of at least 1 equivalent, preferably 1 to 6 equivalents, per equivalent of iron ion.
【００１２】光照射の方法は、できるだけ光が触媒と水
溶液に効率よく照射されなければいけない。人工光源を
用いる場合には内部照射型反応管等のように乱反射光が
再び反応溶液に戻るタイプのセルの使用が望ましい。外
部照射型の場合には光が逃げないようにミラーやアルミ
ホイル等をうまく使用するのがよい。触媒及び水溶液は
マグネチックスターラーや振とう器で激しく撹拌する。
気相は減圧状態が望ましいが、アルゴン等の不活性ガス
で置換しても良い。窓板のガラスの種類は、（１）式の
酸素発生のみ行わせるのであれば可視光透過性のパイレ
ックスやプラスチックなどの安価な素材が使えるが、
（２）式を組み合わせて紫外光を効率よく照射させるた
めには、可視光及び紫外光透過性の石英ガラスなどが望
ましい。In the method of light irradiation, the light must be irradiated to the catalyst and the aqueous solution as efficiently as possible. When an artificial light source is used, it is desirable to use a cell of a type in which irregularly reflected light returns to the reaction solution again, such as an internal irradiation type reaction tube. In the case of an external irradiation type, it is preferable to use a mirror, aluminum foil, or the like so that light does not escape. The catalyst and the aqueous solution are vigorously stirred with a magnetic stirrer or a shaker.
The gas phase is preferably in a reduced pressure state, but may be replaced with an inert gas such as argon. As for the type of glass of the window plate, if only oxygen generation of the formula (1) is performed, an inexpensive material such as Pyrex or plastic which can transmit visible light can be used.
In order to efficiently irradiate ultraviolet light by combining the expressions (2), quartz glass or the like that transmits visible light and ultraviolet light is desirable.
【００１３】[0013]
【実施例】以下に本発明の実施例を述べる。Embodiments of the present invention will be described below.
【００１４】実施例１ 酸化タングステン（関東化学）を0.3g、硫酸鉄(III)を1
mmol及び水400mlを混合して内部照射型反応容器に仕込
み、閉鎖循環系にセットした。気相と液相の空気を脱気
後系内にアルゴンを導入し系内全圧を約35torrとした。
光源は400W高圧水銀灯を用い、触媒をスターラーによっ
て分散させながら光照射した。ランプ冷却管はパイレッ
クス（300nm以下の波長の光をカット）を用いた。生成
した酸素はガスクロマトグラフィー及び圧力計で定性定
量した。酸素生成速度は37.9μmol/h，４時間後の酸素
発生量は270μmolに達した。Example 1 0.3 g of tungsten oxide (Kanto Chemical) and 1 part of iron (III) sulfate
mmol and 400 ml of water were mixed, charged into an internal irradiation type reaction vessel, and set in a closed circulation system. After degassing the air in the gas phase and the liquid phase, argon was introduced into the system to adjust the total pressure in the system to about 35 torr.
A 400 W high-pressure mercury lamp was used as a light source, and light irradiation was performed while dispersing the catalyst with a stirrer. As a lamp cooling tube, Pyrex (cutting light having a wavelength of 300 nm or less) was used. The generated oxygen was qualitatively determined by gas chromatography and a pressure gauge. The oxygen generation rate was 37.9 μmol / h, and the amount of generated oxygen after 4 hours reached 270 μmol.
【００１５】実施例２ 実施例１において、ランプ冷却管と反応溶液との間に紫
外線カットフィルターを取り付け、溶液には400nm以上
の可視光線のみ照射した。酸素生成速度は54.7μmol/
h，４時間後の酸素発生量は343μmolに達した。WO3はバ
ンドギャップが約2.8eVなので440nmまでの可視光線を吸
収することができる。またWO3の伝導帯準位はFe(III)/F
e(II)より高く、価電子帯は酸素発生準位より低い。さ
らにWO3は酸性条件では安定である。以上よりWO3を用い
ると可視光線で（１）式のアップヒル反応を進行できる
ことがわかった。Example 2 In Example 1, an ultraviolet cut filter was provided between the lamp cooling tube and the reaction solution, and the solution was irradiated with only visible light of 400 nm or more. Oxygen generation rate is 54.7μmol /
After 4 hours, the amount of generated oxygen reached 343 μmol. WO 3 can be band gap to absorb visible light up to about 2.8eV, so 440nm. The conduction band level of WO 3 is Fe (III) / F
It is higher than e (II) and the valence band is lower than the oxygen generation level. Furthermore, WO 3 is stable under acidic conditions. From the above, it was found that when WO 3 was used, the uphill reaction of the formula (1) could proceed with visible light.
【００１６】実施例３ 実施例１において、市販品のWO3の代わりに、H2WO4の熱
分解で調製したWO3の触媒活性を調べた。石英容器を使
いマッフル炉で空気焼成を１時間行った。４時間後の酸
素発生量で比較すると５００度までは焼成温度とともに
向上していくが、それ以上温度を上げると発生量は低下
した。初期発生速度で比較すると焼成温度は低温ほど良
かった。高温焼成での活性低下の原因は、シンタリング
による結晶成長にともなう表面積の低下、電荷の拡散距
離の移動、光の触媒への照射効率の減少等が考えられ
る。次表に、WO3を得るためのH2WO4の焼成温度と、得ら
れたWO3を用いた酸素発生速度及び４時間後の酸素発生
量との関係を示す。Example 3 In Example 1, the catalytic activity of WO 3 prepared by thermal decomposition of H 2 WO 4 was examined instead of the commercially available WO 3 . Air calcination was performed for 1 hour in a muffle furnace using a quartz container. Compared with the amount of oxygen generated after 4 hours, the temperature increased with the sintering temperature up to 500 ° C., but when the temperature was further increased, the generated amount decreased. As compared with the initial generation rate, the lower the firing temperature, the better. The causes of the decrease in activity during high-temperature sintering are considered to be a decrease in surface area due to crystal growth due to sintering, a shift in charge diffusion distance, and a decrease in irradiation efficiency of light to the catalyst. The following table shows the relationship between the oxygen generation rate and the oxygen generation amount after 4 hours using a firing temperature of the H 2 WO 4, the resulting WO 3 to obtain WO 3.
【００１７】[0017]
【表１】 [Table 1]
【００１８】実施例４ 実施例１において、WO3の代わりに、In2O3（和光純薬）
を用いた。In2O3はバンドギャップはWO3とほぼ同じ可視
光応答性半導体である。WO3よりは活性が低いが、酸素
発生が見られた。[0018] Example 4 In Example 1, in place of WO 3, In 2 O 3 (Wako Pure Chemical)
Was used. In 2 O 3 is a visible light responsive semiconductor whose band gap is almost the same as WO 3 . Less active than WO 3, but the oxygen evolution was observed.
【００１９】実施例５ 硫酸鉄(II)を1mmol及び水400mlと混合して内部照射型反
応容器に仕込み、閉鎖循環系にセットした。触媒は使用
していない。気相と液相の空気を脱気後系内にアルゴン
を導入し系内全圧を約35torrとした。光源は400W高圧水
銀灯を用い、光照射した。ランプ冷却管は石英（200nm
以下の波長の光をカット）を用いた。生成した水素はガ
スクロマトグラフィー及び圧力計で定性定量した。水素
生成速度は16,6μmol/hに達した。これはFe(II)イオン
の紫外線による光反応で（２）式が進行し、水素が発生
していることが確認される。Example 5 1 mmol of iron (II) sulfate and 400 ml of water were mixed, charged into an internal irradiation type reaction vessel, and set in a closed circulation system. No catalyst was used. After degassing the air in the gas phase and the liquid phase, argon was introduced into the system to adjust the total pressure in the system to about 35 torr. A 400 W high-pressure mercury lamp was used as a light source, and light irradiation was performed. Lamp cooling tube is quartz (200nm
The following wavelengths were cut). The produced hydrogen was qualitatively determined by gas chromatography and a pressure gauge. The hydrogen production rate reached 16.6 μmol / h. This is a photoreaction of Fe (II) ion by ultraviolet rays, and the equation (2) proceeds, and it is confirmed that hydrogen is generated.
【００２０】実施例６ Pt(0.1wt%)-TiO2からなる光触媒を0.3g、硫酸鉄(II)を1
mmol及び水400mlを混合して内部照射型反応容器に仕込
み、閉鎖循環系にセットした。気相と液相の空気を脱気
後系内にアルゴンを導入し系内全圧を約35torrとした。
光源は400W高圧水銀灯を用い、触媒をスタ−ラ−によっ
て分散させながら光照射した。ランプ冷却管はパイレッ
クスを用いた。生成した水素はガスクロマトグラフィー
及び圧力計で定性定量した。水素生成速度は4.1μmol/
h，４時間後の水素発生量は13.1μmolであった。ランプ
冷却管にパイレックスを用い、光触媒なしで行ったとき
には水素はほとんど発生しないことから、これは光触媒
反応で（２）式が進行し、水素が発生していると考えら
れる。Example 6 0.3 g of a photocatalyst composed of Pt (0.1 wt%)-TiO 2 and 1 g of iron (II) sulfate
mmol and 400 ml of water were mixed, charged into an internal irradiation type reaction vessel, and set in a closed circulation system. After degassing the air in the gas phase and the liquid phase, argon was introduced into the system to adjust the total pressure in the system to about 35 torr.
A 400 W high-pressure mercury lamp was used as a light source, and light irradiation was performed while dispersing the catalyst with a stirrer. Pyrex was used for the lamp cooling tube. The produced hydrogen was qualitatively determined by gas chromatography and a pressure gauge. Hydrogen generation rate is 4.1 μmol /
After 4 hours, the amount of generated hydrogen was 13.1 μmol. When Pyrex is used for the lamp cooling tube and hydrogen is hardly generated when the reaction is performed without a photocatalyst, it is considered that this is caused by the progress of equation (2) in the photocatalytic reaction, and hydrogen is generated.
【００２１】実施例７ 実施例６において、触媒としてRuO2(1wt%)-SrTiO3を用
い、レドックスとして硫酸鉄(II)の代わりにK4[Fe(C
N)6]を用いた。水素発生速度は6.3μmol/hであった。Example 7 In Example 6, RuO 2 (1 wt%)-SrTiO 3 was used as a catalyst, and K 4 [Fe (C) was used as a redox instead of iron (II) sulfate.
N) 6 ] was used. The hydrogen generation rate was 6.3 μmol / h.
【００２２】実施例８ 実施例５の石英照射条件下で触媒としてSiCを添加し
た。市販品のSiCの表面はシリカ膜で覆われているの
で、使用直前に高濃度KOH中で煮沸処理によりシリカ膜
を取り除いた。水素発生速度は20.1μmol/hであり、SiC
を使用しないより活性は向上した。Example 8 Under the quartz irradiation conditions of Example 5, SiC was added as a catalyst. Since the surface of the commercially available SiC was covered with a silica film, the silica film was removed by boiling treatment in high-concentration KOH immediately before use. Hydrogen generation rate is 20.1μmol / h, and SiC
The activity was improved compared to not using.
【００２３】実施例９ 実施例１においてランプ冷却管にパイレックスではなく
石英を用いた。反応開始直後はFe(III)が多いためにWO3
上での可視光を含む光触媒反応（１）式により多量の酸
素発生が見られる。しかしFe(II)が反応系内に蓄積して
くると、Fe(II)の光反応による水素発生（（２）式）が
見られるようになり、反応は平衡状態になる。反応開始
６日後の定常状態での水素発生速度は4.6μmol/h、酸素
発生速度は1.7μmol/hであった。Example 9 In Example 1, quartz was used for the lamp cooling tube instead of Pyrex. Immediately after the start of the reaction, WO 3
According to the photocatalytic reaction (1) including visible light, a large amount of oxygen is generated. However, when Fe (II) accumulates in the reaction system, hydrogen generation (Equation (2)) due to the photoreaction of Fe (II) is observed, and the reaction reaches an equilibrium state. Six days after the start of the reaction, the hydrogen generation rate in a steady state was 4.6 μmol / h, and the oxygen generation rate was 1.7 μmol / h.
【００２４】実施例１０ まず最初に実施例５の方法により石英ガラスフィルター
を介した照射下で水素発生を行った。水素発生速度は実
施例５とほぼ同じであった。酸素は発生しなかった。次
にWO3を添加し、パイレックスフィルターで300nm以下の
光をカットして反応を行ったところ、酸素発生のみ進行
し、その発生速度は4.3μmol/hであった。このように触
媒と光の波長を制御して水素と酸素を分離発生できた。Example 10 First, hydrogen was generated under the irradiation through a quartz glass filter by the method of Example 5. The hydrogen generation rate was almost the same as in Example 5. No oxygen was evolved. Next, WO 3 was added, and the reaction was carried out by cutting off light of 300 nm or less with a Pyrex filter. As a result, only the generation of oxygen proceeded, and the generation rate was 4.3 μmol / h. Thus, hydrogen and oxygen could be separated and generated by controlling the wavelengths of the catalyst and light.
【００２５】比較例１ 実施例１の条件において無触媒条件で反応を行った。酸
素発生速度は1.3μmol/hと非常に低かった。Comparative Example 1 The reaction was carried out under the same conditions as in Example 1 without using any catalyst. Oxygen generation rate was very low at 1.3 μmol / h.
【００２６】比較例２ 実施例２の可視光照射条件で、触媒としてTiO2を用い
た。酸素発生はほとんど見られなかった。Comparative Example 2 Under the visible light irradiation conditions of Example 2, TiO 2 was used as a catalyst. Almost no oxygen evolution was observed.
【００２７】比較例３ 実施例５においてパイレックスフィルターを用いて300n
m以下の光をカットした。水素発生はほとんど見られな
かった。Comparative Example 3 In Example 5, 300 n
The light below m was cut. Hydrogen evolution was hardly observed.
【００２８】[0028]
【発明の効果】本発明によれば、太陽光を酸素に変換す
ることができ、紫外光を水素に変換することができる。
そして、両者の方法を組合わせることにより、水を酸素
と水素に分解することができ、これにより、光エネルギ
ーを酸素と水素に変換し、貯蔵することができる。According to the present invention, sunlight can be converted into oxygen, and ultraviolet light can be converted into hydrogen.
Then, by combining both methods, water can be decomposed into oxygen and hydrogen, whereby light energy can be converted into oxygen and hydrogen and stored.
───────────────────────────────────────────────────── フロントページの続き (72)発明者 草間 仁 茨城県つくば市東１丁目１番 工業技術院 物質工学工業技術研究所内 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Jin Kusama 1-1-1, Higashi, Tsukuba, Ibaraki Pref.
Claims (4)
答性の半導体光触媒を接触させるとともに、該半導体光
触媒に可視光を照射して、該水溶液から酸素を発生させ
ることを特徴とする光エネルギーの変換方法。1. A light, comprising: contacting a semiconductor photocatalyst responsive to visible light with an aqueous solution containing iron (III) ions, and irradiating the semiconductor photocatalyst with visible light to generate oxygen from the aqueous solution. Energy conversion method.
射して水素を発生させることを特徴とする光エネルギー
の変換方法。2. A method for converting light energy, comprising irradiating an aqueous solution containing iron (II) ions with ultraviolet light to generate hydrogen.
触させる請求項２の方法。3. The method according to claim 2, wherein an ultraviolet light-responsive semiconductor photocatalyst is brought into contact with the aqueous solution.
答性の半導体光触媒を接触させるとともに、該半導体光
触媒に可視光を照射して、該水溶液から酸素を発生させ
る光エネルギーの変換工程と、鉄(II)イオンを含む水溶
液に紫外光を照射して水素を発生させる光エネルギーの
変換工程からなることを特徴とする光エネルギーの変換
方法。4. An optical energy conversion step of bringing a visible light responsive semiconductor photocatalyst into contact with an aqueous solution containing iron (III) ions and irradiating the semiconductor photocatalyst with visible light to generate oxygen from the aqueous solution. A light energy conversion step of irradiating an aqueous solution containing iron (II) ions with ultraviolet light to generate hydrogen.
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|---|---|---|---|
| JP8241506A JP2876524B2 (en) | 1996-09-12 | 1996-09-12 | Light energy conversion method |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP8241506A JP2876524B2 (en) | 1996-09-12 | 1996-09-12 | Light energy conversion method |
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| Publication Number | Publication Date |
|---|---|
| JPH1087303A true JPH1087303A (en) | 1998-04-07 |
| JP2876524B2 JP2876524B2 (en) | 1999-03-31 |
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ID=17075349
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|---|---|---|---|
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| JP2005199187A (en) * | 2004-01-16 | 2005-07-28 | Tokyo Univ Of Science | Novel z-scheme type visible light active photocatalyst system for perfectly decomposing water and water perfectly decomposing method using the same |
| JP2007061807A (en) * | 2005-08-04 | 2007-03-15 | National Institute Of Advanced Industrial & Technology | Device for activating photocatalyst and method for activating photocatalyst using it |
| WO2012020834A1 (en) * | 2010-08-12 | 2012-02-16 | トヨタ自動車株式会社 | Method and apparatus for production of hydrogen |
| JP2013234077A (en) * | 2012-05-02 | 2013-11-21 | Toyota Industries Corp | Hydrogen production apparatus and hydrogen production method using the same |
| JP2020143013A (en) * | 2019-03-06 | 2020-09-10 | 国立研究開発法人産業技術総合研究所 | Method for producing cycloalkenone using photoelectrochemical reaction system |
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1996
- 1996-09-12 JP JP8241506A patent/JP2876524B2/en not_active Expired - Lifetime
Cited By (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2005199187A (en) * | 2004-01-16 | 2005-07-28 | Tokyo Univ Of Science | Novel z-scheme type visible light active photocatalyst system for perfectly decomposing water and water perfectly decomposing method using the same |
| JP2007061807A (en) * | 2005-08-04 | 2007-03-15 | National Institute Of Advanced Industrial & Technology | Device for activating photocatalyst and method for activating photocatalyst using it |
| WO2012020834A1 (en) * | 2010-08-12 | 2012-02-16 | トヨタ自動車株式会社 | Method and apparatus for production of hydrogen |
| JPWO2012020834A1 (en) * | 2010-08-12 | 2013-10-28 | トヨタ自動車株式会社 | Hydrogen production method and apparatus |
| JP5549732B2 (en) * | 2010-08-12 | 2014-07-16 | トヨタ自動車株式会社 | Hydrogen production method and apparatus |
| US8951497B2 (en) | 2010-08-12 | 2015-02-10 | Toyota Jidosha Kabushiki Kaisha | Method and apparatus for producing hydrogen |
| JP2013234077A (en) * | 2012-05-02 | 2013-11-21 | Toyota Industries Corp | Hydrogen production apparatus and hydrogen production method using the same |
| JP2020143013A (en) * | 2019-03-06 | 2020-09-10 | 国立研究開発法人産業技術総合研究所 | Method for producing cycloalkenone using photoelectrochemical reaction system |
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| Publication number | Publication date |
|---|---|
| JP2876524B2 (en) | 1999-03-31 |
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