JPH1085607A - photocatalyst - Google Patents

Abstract

(57) [Problem] To provide a photocatalyst having a layered structure capable of decomposing water into hydrogen and oxygen by irradiating light. SOLUTION: When the photocatalyst is represented by the general formula (I): ABCO ₄ , in the formula (I), A is at least one element selected from the group consisting of an alkali metal element and hydrogen;
B is lanthanum, and C is one or more elements selected from the element IVa. Further, A is H, Na, K, Rb,
At least one element selected from Cs, wherein C is T
It is preferable to use at least one element selected from i and Zr.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention
The present invention relates to a photocatalyst comprising a composite oxide that generates at least one of hydrogen and oxygen.

[0002]

2. Description of the Related Art At present, various energy sources are used. Fossil fuels such as petroleum and coal have infinite reserves and emit carbon dioxide, nitrogen oxides and sulfur oxides when burned. As a result, carbon dioxide causes global warming, and nitrogen oxides and sulfur oxides cause acid rain and cause environmental destruction.
Further, nuclear power generation has been put into practical use as a new energy source, but has problems such as safety and waste disposal.
Under such circumstances, attention has been paid to hydrogen, which is one of the clean energy sources, as a method for solving the problems of energy resources and the global environment. Hydrogen only turns into water when burned, and does not cause environmental pollution. However, the use of fossil fuel or the like to generate hydrogen is meaningless. Sunlight is inexhaustible, and water is abundant on Earth. Hydrogen can be obtained by decomposing water using the energy of sunlight. One of the means is a photocatalyst for water decomposition. A photocatalyst is a type of semiconductor. When it absorbs energy above its band gap, it generates holes and electrons, and the holes react with water to produce oxygen and hydrogen ions, which react with the electrons to convert hydrogen. Occur. Among the photocatalysts, a substance having a layered structure is known as a useful substance because, unlike a bulky substance, a high catalytic activity can be obtained by using a layer of a layered structure as a site for a water splitting reaction. In other words, the layered material has more catalytically active sites than the bulk material. Furthermore, compared to materials without a layered structure, the distance traveled by holes and electrons is reduced, especially when the direction of movement is perpendicular to the layer plane, resulting in a reduced rate of recombination of holes and electrons. Thus, a high catalytic activity can be obtained. Conventionally, KCa ₂ has a layered structure and exhibits a high catalytic activity.
Substances such as Nb ₃ O ₁₀ and KSr ₂ Nb ₃ O ₁₀ were known, but none of them could decompose water into hydrogen and oxygen.

[0003]

Among the conventional substances having a layered structure, there are few known catalysts for decomposing water into hydrogen and oxygen. Until now, there is no known substance having a layered perovskite structure that can decompose water into hydrogen and oxygen. Accordingly, an object of the present invention is to provide a photocatalyst that has a layered perovskite structure and decomposes water into hydrogen and oxygen using light.

[0004]

The present invention provides a photocatalyst comprising a composite oxide which decomposes water with light to produce at least one of hydrogen and oxygen, and which is represented by the general formula (I): ABCO ₄ And the general formula (I)
Wherein A is one or more elements selected from the group consisting of alkali metal elements and hydrogen, B is lanthanum, and C is one or more elements selected from the element IVa. " A is H, Na, K, Rb,
Preferably, it is at least one element selected from Cs (Claim 2), wherein C is selected from Ti and Zr.
Preferably, the element is at least one kind of element.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The photocatalyst of the present invention is represented by the general formula (I): ABCO ₄ and has a layered structure. Therefore, like the conventional substance, the alkali metal between the layers can be ion-exchanged, and if the ion exchange is performed in an acid aqueous solution, the alkali metal between the layers can be exchanged for proton. The photocatalyst of the present invention is synthesized by a usual solid-phase method, that is, by mixing and sintering oxides or carbonates or nitrates of each metal component as a raw material at a target composition ratio, and then performing other wet methods Alternatively, it may be synthesized by a gas phase method. When A is hydrogen in the general formula (I), a composite oxide of the general formula (I) in which A is an alkali metal is first synthesized,
Thereafter, the composite oxide is ion-exchanged in an aqueous acid solution such as nitric acid to exchange alkali metal ions for hydrogen ions and synthesize. Of course, even when A is an alkali metal other than hydrogen, a composite oxide having a desired composition can be similarly synthesized by an ion exchange reaction. The shape of the photocatalyst of the present invention is desirably particles having a large surface area in order to make effective use of light. Generally, the size of the particles is 0.1 to 10 μm, preferably 0.1 to 1 μm. Conventional means for obtaining such particle sizes include, for example,
There is pulverization by a ball mill. Furthermore, the photocatalyst of the present invention can be modified as commonly used for photocatalyst production, such as supporting Pt or NiO as a cocatalyst.
Further, the catalytic activity can be enhanced by erecting a pillar of an inorganic substance in order to effectively use the interlayer that is a site of the water splitting reaction, or by widening the interlayer distance by ion exchange of alkylammonium. Hereinafter, the present invention will be specifically described, but the present invention is not limited thereto.

(Method for Producing Photocatalyst) A method for producing NaLaTiO ₄ as a specific substance represented by the general formula (I): ABCO ₄ by a solid phase method will be described. First 8.85g of _{Na 2 CO 3, La 2 O} 3 and 2
0.90 g and 10.25 g of TiO ₂ were weighed, each was collected in a platinum crucible, and fired at 1200 ° C. for 10 hours. After firing, this sample was ground in a mortar to a size of 10 μm or less.
When the obtained powdery sample was identified by powder X-ray diffraction, it was confirmed that it was the target substance. Next, a Ni supporting process was performed on the powdery sample. Powder sample 5g
Was immersed in an aqueous nickel nitrate solution containing 3 wt% of nickel for about 1 hour. Thereafter, the impregnated powdery sample was heated in a water bath, and after the water was evaporated, the sample was further heated with a direct fire. Heating was stopped when the powdery sample stopped emitting steam and the powdery sample turned black.

Next, this sample was placed in a pretreatment flask, the flask was connected to a closed circulation system, and the inside of the flask was evacuated. After evacuation, about 300 Torr of hydrogen was introduced, and the bottom of the flask was heated at 500 ° C. for 2 hours while circulating hydrogen.
Thereafter, hydrogen was evacuated, oxygen was introduced at about 150 Torr, and the flask was heated again at 200 ° C. for 1 hour. This treatment was performed to increase the activity of the photocatalyst.

Through the above steps, the Ni-supported photocatalyst NaL
aTiO ₄ is completed. (Evaluation of catalytic activity) For evaluation of the catalytic activity of a photocatalyst for water splitting, a closed circulation catalytic reactor was used. 1 g of the Ni-supported photocatalyst produced by the above method was placed in 400 ml of pure water, and irradiated with light while stirring with a magnetic stirrer. A 450 W high-pressure mercury lamp was used as a light source. A quartz tube was used as the material of the reaction tube. The detection and quantification of the generated hydrogen and oxygen were performed by gas chromatography. As a result of the measurement, generation of hydrogen and oxygen was recognized. The hydrogen generation activity was 9.8 μmol / h, and the oxygen generation activity was 2.9 μm.
ol / h.

The composite oxide NaLaTiO ₄ of the present invention comprises
It is a revolutionary photocatalyst that irradiates light to decompose water and generate both hydrogen and oxygen.

[0010]

As described above, the general formula ABCO _{4 of the} present invention is used.
The photocatalyst represented by can generate both hydrogen and oxygen. Further, since the substance of the present invention has a layer structure, it can be used as a site for a water splitting reaction between the layers.
More hydrogen and oxygen can be generated than the bulk material.

Claims (3)

[Claims] 1. A photocatalyst comprising a composite oxide which decomposes water by light to generate at least one of hydrogen and oxygen, wherein the photocatalyst is represented by the general formula (I): ABCO ₄ ,
Wherein A is at least one element selected from the group consisting of alkali metal elements and hydrogen, B is lanthanum, and C is at least one element selected from the element IVa. photocatalyst. 2. The photocatalyst according to claim 1, wherein A is at least one element selected from H, Na, K, Rb, and Cs. 3. The photocatalyst according to claim 1, wherein said C is at least one element selected from Ti and Zr.