JP4526619B2 - Visible light active photocatalyst - Google Patents

Description

【００４７】
表１及び図６から明らかなように、水熱晶析法酸化鉄包接四チタン酸は、酸化鉄の含有量及び比表面積は、錯体法のものに比べ少ないが、水素生成活性は錯体法のものより約５倍大きかった。これは、水熱晶析反応により包接された酸化鉄の結晶性が高いためであると思われる。
【００４８】
（実施例３）
実施例１と同様にして、四チタン酸を、種々の１Ｍ遷移金属塩の水溶液中で水熱処理し、遷移金属酸化物包接四チタン酸を合成した。得られた遷移金属酸化物包接四チタン酸を、空気中３００℃で１時間仮焼して試料を得た。これらの試料を、６０℃の０．１ＭＮａ₂Ｓ水溶液５００ｃｍ³に添加し、１００Ｗの水銀灯の波長４００ｎｍ以上の可視光を照射した。可視光照射により水の光分解が起こり、水素が発生した。このときの水素生成速度を図７に示す。図７には、使用した遷移金属塩の種類を示し、（ ）内には水熱処理温度を示している。
【００４９】
図７から明らかなように、バナジウム、クロム、マンガン、鉄、ニッケル、銅の水溶液中で水熱晶析反応によりこれらの酸化物を包接したものは、いずれも可視光照射下で水素生成活性を示すことがわかる。
【００５０】
【発明の効果】
本発明に従い、小さなバンドギャップエネルギーを有する遷移金属酸化物を層状チタン酸化合物の層間に包接することにより、可視光で励起可能な優れた光触媒とすることができる。
【００５１】
本発明の可視光活性光触媒は、陽イオン交換性層状チタン酸化合物を遷移金属塩の水溶液に分散させた後、これを水熱処理して水熱晶析反応により陽イオン交換性層状チタン酸化合物の層間に遷移金属酸化物を包接させることにより得ることができる。また、得られた遷移金属酸化物包接層状チタン酸化合物を仮焼することにより、さらに光触媒活性を高めることができる。
【図面の簡単な説明】
【図１】実施例１及び比較例１において合成した四チタン酸カリウム、四チタン酸、及びこれらから合成した酸化鉄包接四チタン酸の粉末Ｘ線回折パターンを示す図。
【図２】実施例１における酸化鉄包接四チタン酸及び比較例１における四チタン酸の紫外−可視拡散反射スペクトルを示す図。
【図３】実施例１において得られた酸化鉄包接四チタン酸の水熱処理温度と水素生成速度との関係を示す図。
【図４】実施例２において仮焼した酸化鉄包接四チタン酸の粉末Ｘ線回折パターンを示す図。
【図５】実施例２において得られた酸化鉄包接四チタン酸の仮焼温度と水素生成速度との関係を示す図。
【図６】実施例２において得られた水熱晶析法酸化鉄包接四チタン酸と比較例２において得られた錯体法酸化鉄包接四チタン酸の水素生成量を示す図。
【図７】実施例３において得られた種々の遷移金属酸化物包接四チタン酸の水素生成速度を示す図。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a photocatalyst, and more particularly to a visible light active photocatalyst that can efficiently advance a photochemical reaction by sunlight.
[0002]
[Prior art and problems to be solved by the invention]
In recent years, a method has been proposed in which a semiconductor is used as a photocatalyst to produce hydrogen by photolyzing water to convert light energy into chemical energy, and a method to photolyze and purify environmental pollutants. Titanium dioxide is known as a typical semiconductor photocatalyst used for such a reaction.
[0003]
However, titanium dioxide has a large band gap energy of about 3 eV, and could not be excited by light having a long wavelength (visible light) of 400 nm or more. As is well known, light (ultraviolet light) having a wavelength of 400 nm or less contained in sunlight is a minute amount of about 5%, and most of the light is visible light having a wavelength of 400 nm or more. Therefore, development of a semiconductor photocatalyst that can be excited by visible light, that is, has high utilization efficiency of sunlight, has been desired.
[0004]
An object of the present invention is to provide a visible light active photocatalyst exhibiting efficient catalytic activity with sunlight.
[0005]
[Means for Solving the Problems]
As a result of diligent research in view of the above problems, the present inventors have become able to excite with visible light when a transition metal oxide is included between layers of a cation-exchange layered titanate compound, and water is efficiently discharged by sunlight. The present invention was completed by finding that hydrogen can be produced by decomposition or that an organic compound can be photocatalytically oxidized and decomposed.
[0006]
That is, the visible light active photocatalyst of the present invention is obtained by dispersing a cation exchange layered titanate compound in an aqueous solution of a transition metal salt, hydrothermally treating it at a temperature of 100 to 200 ° C., and performing hydrothermal crystallization reaction. Oxidation number and crystallinity of transition metal oxide by inclusion of transition metal oxide between layers of cation exchange layered titanate compound and then calcining in air at a temperature of 100 to 500 ° C. It is characterized by adjusting .
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in more detail.
(1) Configuration of Visible Light Active Photocatalyst of the Present Invention The visible light active photocatalyst of the present invention is formed by including a transition metal oxide between layers of a cation exchange layered titanate compound.
[0008]
(A) Cation Exchangeable Layered Titanate Compound Any cation exchangeable layered titanate compound can be used as long as it is a layered titanate compound capable of exchanging cations between layered lattices with cations outside the compound. but good, _{specifically, H 2 Ti 2 O 5,} H 2 Ti 3 O 7, H 2 Ti 4 O 9, H 2 La 2 Ti 3 O 10, H 8x (Fe x Ti 1-x) 8 O _16, HTiNbO ₅ and the like alkali metal salts thereof and alkaline earth metal salts are preferred, _{H 2 Ti 2 O 5, H} 2 Ti 3 O 7, H 2 Ti 4 O 9, H 8x (Fe x Ti 1 _-x ) ₈ O ₁₆ is preferably used.
[0009]
(B) Transition Metal Oxide The transition metal oxide used in the present invention is not particularly limited as long as it is a transition metal oxide, but preferably has a small band gap energy. From such a viewpoint, an oxide of at least one metal selected from vanadium, chromium, manganese, iron, cobalt, nickel, and copper is preferably used.
[0010]
(2) Method for Producing Visible Light Active Photocatalyst of the Present Invention The method for producing the visible light active photocatalyst of the present invention is not particularly limited. For example, a cation exchange layered titanate compound is used as an aqueous solution of a transition metal salt. After being dispersed in the solution, it can be produced by hydrothermally treating and encapsulating a transition metal oxide between the layers of the cation exchange layered titanate compound by a hydrothermal crystallization reaction. Hereinafter, this manufacturing method will be described with examples.
[0011]
(A) Synthesis of cation-exchange layered titanate compound K ₂ CO ₃ and TiO ₂ are mixed at a predetermined molar ratio and calcined at 800 to 1500 ° C. for 1 to 240 hours to synthesize potassium titanate. When synthesizing titanate compounds other than potassium salts, K ₂ CO ₃ is replaced with other metal oxides or metal carbonates. In addition to the solid phase method, synthesis by a flux method or a hydrothermal method is also possible. When the layered titanate compound is ion-exchanged in mineral acid, interlayer metal ions can be exchanged for hydrogen ions.
[0012]
(B) Inclusion of transition metal oxide A layered titanic acid compound is suspended in an aqueous solution containing a predetermined amount of transition metal ions and subjected to hydrothermal treatment at a temperature of 100 to 200 ° C. for 0.5 to 10 hours to form layered titanic acid. The transition metal oxide is included between the compound layers. The preferable temperature range of the hydrothermal treatment is appropriately selected depending on the transition metal to be used, the pH in the hydrothermal reaction, the type of solvent, and the like.
[0013]
In addition, after dispersing a layered titanic acid compound in an organic solvent such as n-hexane or water, an alkylamine such as n-C ₈ H ₁₇ NH ₂ or n-C ₃ H ₇ NH ₂ is added, and the room temperature or higher In addition, when the reaction is performed at a temperature lower than the boiling point of the solvent for 1 to 240 hours and the cation between layers is previously ion-exchanged with an alkylammonium ion, the interlayer inclusion reaction of the transition metal oxide can be efficiently performed. . Further, the layered titanate compound that includes the obtained transition metal oxide is calcined in air at a temperature of, for example, 100 to 500 ° C., so that the oxidation number and crystallinity of the transition metal oxide between the layers are increased. Can be adjusted. Thereby, the photocatalytic activity can be further improved.
[0014]
In general, since the hydrolysis reaction of metal ions represented by the following formula is promoted under hydrothermal conditions, it is known that transition metal oxides can be crystallized by hydrothermal treatment of an aqueous transition metal salt solution. It was.
[0015]
M ^{n +} + nH ₂ O → MO _{n / 2} + nH ⁺ + n / 2H ₂ O
However, the present inventors have found that this crystallization reaction proceeds particularly rapidly between layers of the layered compound than in the solution. The present invention utilizes this to selectively deposit and include the transition metal oxide only between the layers of the layered titanate compound.
[0016]
The photocatalyst of the present invention includes at least one kind of ultrafine particles of transition metal oxide having a particle size of 1.0 nm or less, and has a large specific surface area and a small band gap of 3 eV or less. Therefore, it can be suitably used for a photocatalytic reaction using sunlight.
[0017]
(3) Photolysis using the photocatalyst of the present invention The photocatalyst of the present invention can be used for oxidation of organic substances and inorganic compounds by photochemical reaction, hydrogen production by decomposition of water, and the like. Hereinafter, an example of a method for producing hydrogen using the photocatalyst of the present invention will be described.
[0018]
The aqueous solution to be subjected to photolysis may be pure water (not containing no impurities but water containing no sacrificial reducing agent such as an organic substance that reacts with holes), but a reducing alkali compound. It is preferable to use an aqueous solution, an alcohol aqueous solution, or the like, or a mixed aqueous solution thereof may be used. As the reducing alkali compound, Na ₂ S, Na ₂ SO ₃ , Na ₂ S ₂ O ₃ , NaNO _{2 and the} like are preferable, and a mixture thereof may be used. The concentration is preferably from 0.01 to 1 mol / liter. Moreover, as alcohol, methanol, ethanol, propanol, 2-aminoethanol etc. are preferable, and these mixtures may be sufficient. The concentration is preferably 0.01 to 1 mol / liter.
[0019]
The photocatalyst of the present invention is added to the aqueous solution. The addition amount of the photocatalyst is preferably 0.5 to 50 mg / cm ^3, in particular 1-3 mg / cm ³ are preferred. Thus, by irradiating light to the aqueous solution to which the photocatalyst is added, water is decomposed and hydrogen is generated. The wavelength of the irradiated light is preferably 550 nm or less. Since the wavelength of sunlight is about 350 to 2000 nm, sunlight may be irradiated in the present invention. The temperature of the aqueous solution is preferably 25 to 60 ° C.
[0020]
As described above, the photocatalyst of the present invention is useful as a photocatalyst in the production of hydrogen by decomposing water, but the photocatalyst of the present invention is not limited to such applications. It can also be used as a catalyst for organic matter synthesis reaction and a decomposition reaction for harmful substances.
[0021]
Examples of harmful substances include substances that may adversely affect the human body and living environment, and substances that may have a potential, such as various biological oxygen demand substances, air pollutants, herbicides, bactericides, insecticides, and the like. Substances such as pesticides, microorganisms such as bacteria, actinomycetes, fungi, algae, and molds, cigarette dust, odors, pet odors, malodorous gases, and human urine odors. Examples of environmental pollutants include organic halides, organic phosphorus compounds and other organic compounds, nitrogen compounds, sulfur compounds, cyanide compounds, and chromium compounds. Specific examples of the organic halogen compound include polychlorinated biphenyl, chlorofluorocarbon, trihalomethane, trichloroethylene, and tetrachloroethylene. Other than organic halogen compounds, hydrocarbons such as surfactants and oils, aldehydes, mercaptans, alcohols, amines, amino acids, proteins and the like can be exemplified. Examples of the nitrogen compound include ammonia, nitrogen oxide (NO _x ), sulfur oxide (SO _x ), and the like.
[0022]
The photocatalyst of the present invention can also be used for hydrophilicity imparting reaction. By utilizing this hydrophilicity imparting reaction, it is possible to prevent the mirror, glass, glasses and the like from being fogged and to prevent the outer wall from being stained. In addition, cancer cells can be treated using an endoscope or the like.
[0023]
The photocatalyst of the present invention can be used in various ways. For example, the photocatalyst of the present invention is contained in the substrate, a coating liquid containing the photocatalyst of the present invention is applied to the substrate surface to form a film, or a film containing the photocatalyst of the present invention is formed on the substrate surface. It can be used by laminating.
[0024]
Examples of the base material include ceramic, ceramic, metal, glass, plastic, wood, or a composite thereof. The shape of the base material may be any shape, and it may be a simple shape such as a spherical object, a cylindrical object, a cylindrical object, a tile, a wall material, a floor material such as a flooring material, a sanitary ware, a wash basin, a bathtub, a sink. It may be a complicated shape. Others, curve mirrors, signs, reflectors, tunnel interior plates, tunnel lighting, exterior walls, roofs, sashes, mirrors, showcases, refrigerated / frozen showcases, show windows, signboards, glass greenhouses, vinyl houses, displays, solar cells, It can be used for spectacles, optical lenses, endoscope lenses, paints, interior members and the like. The substrate surface may be porous or dense.
[0025]
When it is contained in the substrate, examples of the inorganic binder include silicate glass, borate glass, phosphate glass, and general ceramic glaze frit. For example, the photocatalyst of the present invention is dispersed in a binder liquid composed of SiO ₂ —Al ₂ O ₃ —Na ₂ O / K ₂ O frit, and the photocatalyst is attached to the substrate so that part of the photocatalyst is exposed from the binder layer. Then, after heating to melt the binder layer, the multifunctional substrate containing the photocatalyst of the present invention is obtained by cooling to solidify the binder layer.
[0026]
A coating liquid containing a photocatalyst is obtained by mixing a photocatalyst and a binder for coating liquid. As the coating liquid binder, a binder resistant to photocatalytic activity is desired, and examples thereof include siloxane resin, silicon resin, fluororesin, and silicate glass. Moreover, in order to utilize the photocatalyst mixed in the layer more effectively, what has translucency as a binder is more suitable. Further, in view of the point that it is difficult to get dirt, those having water repellency such as siloxane resin and fluororesin are preferable.
[0027]
The coating liquid can be applied by a usual method, and examples thereof include spray coating, dip coating, roll coating, and spin coating. In the case of forming a film by coating on the surface of the base material, a layer having a photocatalytic action may be formed on the entire surface of the base material, or may be formed by coating a part thereof. Moreover, the coating liquid containing a photocatalyst may be applied directly to the substrate, or may be applied via a primer layer. In particular, when the substrate is metal or glassy, it is preferable to use a primer layer in order to improve the adhesive strength.
[0028]
A film containing a photocatalyst is obtained by spraying a mixture of a photocatalyst and a binder on a release paper so that a part of the photocatalyst is exposed from the binder layer, curing or drying, and then peeling the release paper. It is not limited to this.
Next, the obtained film is laminated or stuck on the base material, heated to melt the binder layer, and then cooled to obtain a multifunctional member in which a film containing a photocatalyst is laminated on the surface of the base material. be able to.
[0029]
[Action]
The band gap energy of the layered titanate compound is 3.2 to 3.5 eV and does not show photocatalytic activity when irradiated with visible light, but the photocatalyst of the present invention has a band gap of about 2.0 to 3.3 eV. It is excited by irradiation with light having a wavelength of about 375 to 650 nm, and shows high catalytic activity by visible light. This is because the inclusion transition metal oxide has a small band gap energy that can be excited by visible light.
[0030]
The transition metal oxide alone has very low photocatalytic activity. However, inclusion of the transition metal oxide between the layers results in ultrafine particles having a particle size of 1 nm or less and increases the effective reaction surface area. In addition, the photocatalyst is produced because electrons or holes generated by photoexcitation of the transition metal oxide move to the titanate compound in the host layer, thereby effectively separating charges and suppressing recombination of electrons and holes. Activity is improved. In addition, the photocatalyst of the present invention hardly chemically dissolves in an aqueous solution and is chemically stable.
[0031]
【Example】
Examples The present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples.
[0032]
Example 1
K ₂ CO ₃ and TiO ₂ were mixed at a molar ratio of 1: 2.5, and calcined at 1300 ° C. for 5 hours to synthesize potassium tetratitanate (K ₂ Ti ₄ O ₉ ). 1 g of this potassium tetratitanate powder is dispersed in 1 M FeSO ₄ containing 5 times the ion exchange capacity of Fe ²⁺ , hydrothermally treated at 120-250 ° C. for 12 hours, filtered and separated to contain iron oxide-clad tetra-titanium. The acid was obtained. In addition, potassium tetratitanate powder was dispersed in a 1 M hydrochloric acid aqueous solution at 30 ° C. for 30 minutes to synthesize tetratitanic acid (H ₂ Ti ₄ O ₉ ), and 1 g of this tetratitanate powder was 5 times the ion exchange capacity. It was dispersed in 1M FeSO ₄ containing Fe ²⁺ , hydrothermally treated at 120 to 250 ° C. for 12 hours, and then separated by filtration to obtain iron oxide clathrate tetratitanate.
[0033]
The powder X-ray diffraction patterns of these samples obtained by hydrothermal treatment at 120 ° C. are shown in FIG. Further, FIG. 2 shows an ultraviolet-visible diffuse reflection spectrum of iron oxide clathrate tetratitanate obtained by hydrothermal treatment of titanic acid.
[0034]
A sample of 0.5 g of iron oxide clathrate tetratitanate obtained by hydrothermal treatment at 120 ° C., 150 ° C., 200 ° C., and 250 ° C. is added to 500 cm ³ of a 0.1 M Na ₂ S aqueous solution at 60 ° C., and 100 W The visible light having a wavelength of 400 nm or more of the mercury lamp was irradiated. Hydrogen was decomposed by visible light irradiation and hydrogen was generated. The relationship between the hydrogen production rate (hydrogen production activity) and the hydrothermal treatment temperature at this time is shown in FIG.
[0035]
(Comparative Example 1)
The powder X-ray diffraction patterns of potassium tetratitanate and tetratitanate synthesized in Example 1 are shown in FIG. Moreover, the ultraviolet-visible diffuse reflection spectrum of tetratitanic acid is shown in FIG.
[0036]
0.5 g of a sample of potassium tetratitanate and tetratitanate was added to 500 cm ³ of a 0.1 M Na ₂ S aqueous solution at 60 ° C., and irradiated with visible light having a wavelength of 400 nm or more from a 100 W mercury lamp. With visible light irradiation, no photocatalytic activity was observed, and the hydrogen production reaction did not proceed at all. The experiment at a water treatment temperature of 25 ° C. in FIG. 3 means these samples.
In addition, AE in FIG.1, FIG2 and FIG.3 is as follows.
[0037]
A: Iron oxide clathrate tetratitanic acid obtained by hydrothermal treatment of potassium tetratitanate in 1 M FeSO ₄ aqueous solution at 120 ° C.
B: Iron oxide clathrate tetratitanic acid obtained by hydrothermal treatment of tetratitanic acid in 1 M FeSO ₄ aqueous solution at 120 ° C.
C: Potassium tetratitanate D: Tetratitanate E: α-Fe ₂ O ₃
[0038]
As is clear from FIG. 1, both iron oxide clathrate tetratitanates A and B show an X-ray diffraction pattern similar to that of tetratitanate D. As is clear from FIG. 2, tetratitanic acid D has an upper absorption edge wavelength of 400 nm and is not excited by visible light having a wavelength of 400 nm or more, but iron oxide clathrate tetratitanate B has a visible wavelength of 400 to 600 nm. It absorbs light and can be excited with visible light.
[0039]
Further, as is apparent from FIG. 3, potassium tetratitanate and tetratitanic acid shown at a hydrothermal treatment temperature of 25 ° C. did not show photocatalytic activity when irradiated with visible light having a wavelength of 400 nm or more, and hydrogen generation was not observed. Iron oxide clathrate tetratitanates A and B showed photocatalytic activity when irradiated with visible light, and produced hydrogen from an aqueous Na ₂ S solution.
[0040]
(Example 2)
In Example 1, the iron oxide clathrated tetratitanic acid synthesized by hydrothermal treatment of tetratitanic acid in an aqueous 1 M FeSO ₄ solution at 120 ° C. was each heated at 100 ° C., 300 ° C., 500 ° C., and 1000 ° C. for 1 hour in air. It was calcined. The powder X-ray diffraction pattern of the obtained sample is shown in FIG.
[0041]
0.5 g of these samples were added to 500 cm ³ of a 0.1 M Na ₂ S aqueous solution at 60 ° C., and irradiated with visible light having a wavelength of 400 nm or more from a 100 W mercury lamp. Visible light photolysis caused water to generate hydrogen. FIG. 5 shows the relationship between the calcining temperature of the sample and the hydrogen generation rate.
[0042]
As is clear from FIG. 4, the X-ray diffraction peak of tetratitanic acid decreased with increasing calcining temperature and disappeared at 1000 ° C. On the other hand, peaks of monoclinic titanium dioxide and anatase appeared at 300 to 500 ° C., and peaks of anatase, rutile and KFeO ₂ were observed at 1000 ° C.
[0043]
As is clear from FIG. 5, the photocatalytic activity of iron oxide clathrate tetratitanate is remarkably improved by calcining in air at 300 ° C., and the hydrogen production rate in the Na ₂ S aqueous solution is the same as that before calcining. It is 3.5 times the sample. This is because iron oxide clathrate tetratitanate obtained by hydrothermal crystallization reaction of iron sulfate contains a lot of low-order iron oxides such as FeO having low photocatalytic activity, and FeC having high catalytic activity by calcination. _This is considered to be due to oxidation to ₂ O ₃ . The reason why the activity decreased when calcined at a higher temperature is considered to be because the layered structure of tetratitanic acid was destroyed.
In this example, a sample obtained by calcining in air at 300 ° C. is referred to as hydrothermal crystallization iron oxide clathrate tetratitanate.
[0044]
(Comparative Example 2)
After dispersing tetratitanate in water was added 5 volumes of n-C ₃ H ₇ NH ₂ four titanate ion exchange capacity, allowed to react for 3 days at 50 ° C., the H ⁺ of interlayer C ₃ H ₇ Ion exchanged with NH ₃ ⁺ . The resulting compound was dissolved in an aqueous solution of [Fe ₃ (OCOCH ₃ ) ₇ OH ₂ H ₂ O] NO ₃ (20 times the amount to be ion-exchanged [Fe ₃ (OCOCH ₃ ) ₇ (OH) 2 H ₂ O]). ⁺ ), And reacted at 50 ° C. for 3 days to obtain [Fe ₃ (OCOCH ₃ ) ₇ OH ₂ H ₂ O] ₂ Ti ₄ O ₉ . The obtained compound was dispersed in water and irradiated with ultraviolet rays with a 500 W mercury lamp for 10 hours to obtain tetratitanic acid containing iron oxide between layers. The obtained sample is referred to as complex method iron oxide clathrate tetratitanate.
[0045]
Table 1 shows the iron content and specific surface area of hydrothermal crystallization iron oxide clathrate tetratitanate in Example 2 and complex iron oxide clathrate tetratitanate in Comparative Example 2. In addition, 0.5 g of these samples are added to 500 cm ³ of a 0.1 M Na ₂ S aqueous solution at 60 ° C., irradiated with visible light having a wavelength of 400 nm or more from a 100 W mercury lamp, and the amount of hydrogen generated by photolysis of water is shown. It is shown in FIG. In FIG. 6, F represents hydrothermal crystallization iron oxide inclusion tetratitanate, and G represents complex iron oxide inclusion tetratitanate.
[0046]
[Table 1]

[0047]
As is apparent from Table 1 and FIG. 6, the hydrothermal crystallization method iron oxide clathrate tetratitanic acid has less iron oxide content and specific surface area than the complex method, but the hydrogen generation activity is complex method. It was about 5 times larger than the one. This is presumably because the crystallinity of the iron oxide included by the hydrothermal crystallization reaction is high.
[0048]
(Example 3)
In the same manner as in Example 1, tetratitanic acid was hydrothermally treated in aqueous solutions of various 1M transition metal salts to synthesize transition metal oxide clathrate tetratitanate. The obtained transition metal oxide clathrate tetratitanic acid was calcined in air at 300 ° C. for 1 hour to obtain a sample. These samples were added to 500 cm ³ of a 0.1 M Na ₂ S aqueous solution at 60 ° C., and irradiated with visible light having a wavelength of 400 nm or more from a 100 W mercury lamp. Visible light photolysis caused water to generate hydrogen. The hydrogen production rate at this time is shown in FIG. FIG. 7 shows the type of transition metal salt used, and the hydrothermal treatment temperature is shown in parentheses.
[0049]
As is clear from FIG. 7, all of these oxides included in an aqueous solution of vanadium, chromium, manganese, iron, nickel, and copper by hydrothermal crystallization reaction under hydrogen irradiation activity under visible light irradiation. It can be seen that
[0050]
【The invention's effect】
According to the present invention, an excellent photocatalyst that can be excited by visible light can be obtained by including a transition metal oxide having a small band gap energy between layers of a layered titanate compound.
[0051]
The visible light active photocatalyst of the present invention is obtained by dispersing a cation exchange layered titanate compound in an aqueous solution of a transition metal salt, hydrothermally treating the cation exchange layered titanate compound by hydrothermal crystallization reaction. It can be obtained by including a transition metal oxide between layers. Moreover, the photocatalytic activity can be further enhanced by calcining the obtained transition metal oxide inclusion layered titanate compound.
[Brief description of the drawings]
1 is a graph showing a powder X-ray diffraction pattern of potassium tetratitanate synthesized in Example 1 and Comparative Example 1, tetratitanic acid, and iron oxide clathrate tetratitanate synthesized therefrom. FIG.
2 is a graph showing ultraviolet-visible diffuse reflectance spectra of iron oxide clathrate tetratitanate in Example 1 and tetratitanate in Comparative Example 1. FIG.
3 is a graph showing the relationship between the hydrothermal treatment temperature of the iron oxide clathrate tetratitanate obtained in Example 1 and the hydrogen production rate. FIG.
4 shows a powder X-ray diffraction pattern of iron oxide clathrate tetratitanate calcined in Example 2. FIG.
5 is a graph showing the relationship between the calcining temperature of iron oxide clathrate tetratitanate obtained in Example 2 and the hydrogen production rate. FIG.
6 is a graph showing hydrogen generation amounts of hydrothermal crystallization iron oxide inclusion tetratitanate obtained in Example 2 and complex iron oxide inclusion tetratitanate obtained in Comparative Example 2. FIG.
7 is a graph showing hydrogen production rates of various transition metal oxide clathrate tetratitanates obtained in Example 3. FIG.

Claims (3)

After the cation-exchange layered titanate compound is dispersed in an aqueous solution of a transition metal salt, this is hydrothermally treated at a temperature of 100 to 200 ° C., and hydrothermal crystallization reaction is performed between the layers of the cation-exchange layered titanate compound. Visible light activity characterized by adjusting the oxidation number and crystallinity of the transition metal oxide by inclusion of a transition metal oxide and then calcining in air at a temperature of 100 to 500 ° C. photocatalyst.   The visible light active photocatalyst according to claim 1, wherein the transition metal oxide is an oxide of at least one metal selected from vanadium, chromium, manganese, iron, cobalt, nickel, and copper. Cation exchanging layered titanic acid _{compound, H 2 Ti 2 O 5,} H 2 Ti 3 O 7, H 2 Ti 4 O 9, H 2 La 2 Ti 3 O 10, H 8x (Fe x Ti 1-x) The visible light active photocatalyst according to claim 1 or 2, which is at least one compound selected from the group consisting of ₈ O ₁₆ , HTiNbO ₅ and alkali metal salts and alkaline earth metal salts thereof.

Images